Notes

* AcquiredPoisonImmunity: Supplement ''Mysteries of the Hollow Earth''. Cannibal tribes are known for their skill in creating poisons. Some of them include small doses of poison in their meals to build up an immunity to them.
* ActionInitiative:
** What Initiative and its rating are for. You roll it once per the entire combat and set the order of actions from lowest to highest values.
** Alternative rules, Continuous Combat, turn Initiative to a counter for when the next move will happen, rather than just an order, so against particularly slow, ambushed or simply unlucky enemies, it is possible to move ''twice'' before they will even have a chance to react.
* AmuletOfDependency: IIt's either carrying an Atlantean gizmo or a fetish made by a voodoo priest... or [[PowerAtAPrice you must offer blood to even use magic]]. ''Lots'' of blood.
* AncientConspiracy: The Terra Arcanum is a secret organization created by the Atlanteans to prevent humanity from finding out about or entering the Hollow Earth. Over the centuries they have become a network of power brokers who control the Earth's leaders and institutions.
* AnimateDead: The more decayed the body, the harder it gets, so things like DemBones are ''incredibly'' hard to create and maintain, but freshly slain targets can be whisked back at the drop of a hat. Beware of characters like voodoo priests, for they might bring back slain guards without any effort.
* AnnoyingArrows: ZigZagged. Bows are on par with most pistols when it comes to pre-definied damage, but since the actual damage comes from combination of Stat, Skill, Specialisation and ''then'' the Damage Rating of the weapon itself, arrows can be just as lethal as anything else. If this wasn't enough, arrows tend to be volleyed [[ChasedByAngryNatives while escaping from natives]], so their (theoretical) low damage very quickly can add up, as [[DeathOfAThousandCuts continuous attacks face less and less Defense with each attempt in the same round]].
* ArmorIsUseless: Nope. An actual, antiquated set of armour, or even ChainmailBikini of the Amazons, is more than enough to make it impossible to hit, regardless of source. And that without brining up remains of Atlantean technology or [[PoweredArmor some high-tech gizmos]]. When a shield-bearer is also wearing a set of armour, they synergise, for really high defensive values.
* ArrowsOnFire: They deal -1 damage (which is a significant debuff by the game standards), but can obviously set things on fire.
* AutoDoc: The ''Secrets of the Surface World'' supplement had an Auto-Doctor as a possible Weird Science gadget.
* AwesomeButImpractical:
** In the baseline game, almost all of the Resources were great for roleplaying (especially when gained during the gameplay, rather than from character generation), and lacked ''any'' practical application, since the default state for characters was being trapped inside the Hollow Earth itself, thus rendering things like Wealth, Fame or Contacts completely superfluous, requiring to outright ignore the setting itself to make them useful for anything. Thankfully, ''Secrets of the Surface World'' salvaged most of them (especially Rank, as it formalised mechanics for secret organisations, along with putting forth lore for pre-existing ones). But even then, Status remained a roleplaying gimmick: for 15 (and its multiplications, up to 75) experience points, your character is recognised in-universe as an esteemed professional and gains an income source from their profession - which pales in comparison with what Wealth does. A single rank of Wealth and Fame does what takes 3 ranks of Status.
** Short for highly specific circumstances and even more specific builds, DualWielding is just not worth it. On paper, it allows two attacks per round or [[SwordAndGun just swapping between two vastly different weapons]] without wasting a round to do so. In reality, it applies penalties so high, you are more likely to miss your attacks completely.
* AwesomenessByAnalysis:
** Variety of scholarly skills provide just as many benefits, both in non-combat and combat situations, simply by providing big bonus to other actions (often party-wide) after successfully analysing or deducting something.
** Talent "Calculated Defense" uses characters Intelligence instead of standard Dexterity to provide Defense rating. In other words - your character evaluated the situation and parried incoming blow due to reading opponents tactics, rather than being good in combat.
* BadPowersGoodPeople: Necromancy itself is very ambigious: it starts out relatively harmless, but then goes through things like curses, causing harm or [[TheLastOfTheseIsNotLikeTheOthers even summoning an]] EldritchAbomination. But it can be freely used by even by [[IncorruptiblePurePureness the purest of heart characters]], as long as they know how to cast it.
* BareHandedBladeBlock: It is possible to perform a Brawl-related Block action against an attack with a Melee weapon, although it suffers a -2 penalty.
* BeenThereShapedHistory:
** TTerra Arcanum actively meddled in the affairs of the world since there has been any kind of human civilization. Various events, but also political plays, assassinations, wars, destruction of specific places etc., were all their doings, either as {{Masquerade Enforcer}}s or because they considered this or that group, country or ''an entire civilisation'' was getting too far ahead of itself.
** Likewise, much of human knowledge and scientific progress was accomplished by an early version of the Order of the Prometheus and then safeguarded by them during the Dark Ages, after which they spearheaded the Renaissance.
* BeethovenWasAnAlienSpy: Since at least the Renaissance, all the prominent scientists and philosophers were members of the Order of Prometheus or were invited to join it.
* BigEater: Supplement ''Mysteries of the Hollow Earth''. Any character with the Flaw of Ravenous must eat twice as much as normal or suffer from the effects of starvation.
* BlackMagic: Necromancy school of magic. It starts relatively harmless, simply allowing to perform a SpookySeance to summon a spirit, but things go very dark very fast from there.
* BlastingItOutOfTheirHands: As one of the basic moves for Called Shots, no less!
* BloodMagic: Magic runs almost literally on blood that has to be sacrificed to cast spells. It makes no difference who or what is the source, as long as it is drained out of sufficient amount of ichor. Once the magic is done, the blood ''burns out'', leaving only oily soot behind.
* BlownAcrossTheRoom: If the damage dealt by the attack exceeds Strength of the target, they are sent flying back. This is particularly useful when having a dramatic battle at a cliffside or when [[GoodOldFisticuffs using your fists]].
* BoringButPractical:
** Hunting rifles. Cheap, reliable, long-ranged, but also bog-standard, without any weird or special features. This is part of what makes them so good - they are easier to repair and they almost never misfeed, which is a common issue with automatic weapons, requiring to clear the jam.
** Martial Arts from ''Secrets of the Surface World'' also include very mundane boxing and savate. While they lack the sheer awesomeness of other martial arts, they are just as effective to use in fight. If not ''more'' effective, since they have no extra requirements for all the flashy stuff.
* BrandishmentBluff: The game outright suggest to use Performance for this in combat situations. Who knows - maybe the {{Mooks}} will not feel lucky to see if your gun is loaded or if you actually have a gun, rather than just [[FingerGun jabbing their back with a finger]].
* BrotherSisterIncest: Supplement ''Mysteries of the Hollow Earth''. In the city of El Dorado the royal family are all descended from the Sun God. It is common for brothers and sisters to marry each other and have children to preserve their bloodline.
* CargoCult: Supplement ''Mysteries of the Hollow Earth''. Cargo cultist tribes live by collecting items from the surface world that reach the Hollow Earth as flotsam and jetsam or inside beached ships or crashed airplanes. They worship the gods that they believe send them the items and even create "landing fields" to encourage them to send more.
* CastFromHitPoints:
** One of the ways to use magic at all is to simply sacrifice own blood. It's not advised, for obvious reasons, but it allows to draw power in a pinch, when lacking a proper sacrifice. Also, characters can simply enhance the effect of their spells, gaining +2 to Sorcery rating for each point of non-lethal damage taken. Interestingly, while normally reaching 0 HP via non-lethal damage would render a character unconscious, when casting spells, the casting takes precedence, so characters will dramatically fall to the ground ''after'' doing some serious magic.
** Alchemical items in the supplement ''Mysteries of the Hollow Earth''.
*** The Life Channeling enchantment allows the user to power the item by inflicting either nonlethal damage on themselves or lethal wounds on other creatures.
*** Blood Offering drawback. An item recharges its powers (so they can be cast again) by inflicting lethal wounds on other creatures.
*** Exhausting drawback. Each time an item is used it inflicts a point of non-lethal damage on the user.
*** Toxic drawback. Each time an item is used it inflicts a point of lethal damage on the user.
* ChainmailBikini: Yes, the Amazons wear those. Well, Plate Bikini, to be specific. It's far less funny when you have to face them in combat, since it works just like any other high-grade armour.
* ChurchMilitant: Ordo Umbra, responsible for all the dirty work that has to be done for or in the name of the Catholic Church. By all accounts, it's a modern take on a knight order, but instead of soldiers, they mostly produce deadly spies.
* CombatTentacles: Supplement ''Mysteries of the Hollow Earth''
** The Kraken is a 100 foot long GiantSquid with tentacles powerful enough to tear open a ship.
** The Giant Octopus has eight tentacles that can grapple and damage opponents.
* ComeWithMeIfYouWantToLive: This StockPhrase is used by Erich Reinhardt in the adventure "Prisoner of the Reich" in the ''Secrets of the Surface World'' supplement.
* CoolButInefficient:
** The selection of unique talents that increase the rating of related stats (for example, Agile offering +1 Dexterity rating) is only worthwhile if said stat is already at 3 or higher. Otherwise, the cost of the talent will be greater than simply raising the related stat to 3. And if you have a stat on 3 or 4, why would you even need to add +1 to it with a Talent, and a unique one at that?
** Instant Reload, an unique Talent (thus only viable for picking during character creation), sounds like the coolest thing ever, as it allows your character to [[ExactlyWhatItSaysOnTheTin instantly reload all firearms without costing an action]]. But short of the Archaic subclass, all firearms present in the game come with magazines or drums and before your gun will run dry, the combat might as well be over. ''Then'' there is the question if your character even has spare bullets left to reload in the first place.
** Flurry and Rapid Shot, as special attacks, rather than Talents. They allow for multiple attacks per round, but with such a high penalty, it's either complete desperation or investing in the related Talents, under same name, to remove the penalty. The total investment to make multiple attacks viable means you can simply use AreaOfEffect weapons or attacks, get a better weapon or simply specialise in a given skill to not ''require'' multiple attacks to drop your targets dead.
** Kip Up, another unique Talent, offers the option to get up from the ground without taking an action after being knocked down. It can only be obtained during chargen. And it's a Talent, so it's worth 15 experience points. To make things even worse, you can instead get Dodge or Parry as a Talent and thus have related actions count as reflexive (read: free action), so you won't even ''be'' knocked down in the first place. Overall, it's a highly situational gimmick, but made ten times worse because of the unique status.
** Jack of All Trades, a Talent from ''Secrets of the Surface World'', is ''incredibly'' inefficient. For 15 experience points, your character removes the -2 penalty for rolling a skill they otherwise possess at 0. At rank 2 of the Talent (and 30 experience), characters gain a +1 to related rolls. Meanwhile, for 30 experience, you can raise 15 different skills (out of the total of 35 there are in the game) to 1, and you don't have to hoard those points, but spend them freely every time you have just 2. Plus of course there are skills you gain during character creation, further decreasing utility of [=JoAT=]. There is a very narrow window where the talent is a solid pick (it enables the use of specialist skills without having the actual specialisation, which is handy for skills like Pilot or Craft), but there are simply better ways to use those points and[=/=]or starting Talent.
** While Followers, a Resource type, are part of a game-breaking combination when used by Allies (another Resource type), on their own, they are not worth their price. They are much weaker than Allies (while costing the exact same amount of points) and their main advantage is in their numbers. In particular, when picking Followers as just a single, but stronger character, you are buying an Ally without the advantages of one (namely - a starting Resource/Talent slot).
* CreepyCentipedes: Supplement ''Mysteries of the Hollow Earth''
** The ''Arthropleura'' is 6 foot long, has 50 pairs of legs and a vicious bite.
** The giant centipede grows up to ten feet long and two feet wide and has a pair of forcipules (poison-injecting pincers).
* CriticalExistenceFailure: Averted. Not only the game tracks separately lethal and non-lethal damage, but hitting 0 Health isn't equal with dying - that will just render a character unconscious. Only reaching -5 Health will finally kill someone. On top of that, the Diehard Talent not only extends the threshold to -7, but also prevents the whole unconscious part.
* CriticalFailure: Rolling 0 successes in a check means a critical failure. The severity of it is tied to how difficult the initial task was: an easy task will cause some trivial issue, but a tough one might prevent entirely a retry (breaking a lock in a door when trying to pick it) or even cause a dramatic catastrophe (crash-landing a plane during a storm).
* CutscenePowerToTheMax: The logic behind Style points, particularly when they are used to boost Talents or shrug off damage. For the rest of the scene (or the whole combat encounter), a Talent rank can be temporarily increased, a dangerous amount of lethal damage can be ignored or more dice can be rolled for a crucial skill check. The power-up lasts only for the duration of that specific bit of the scenario, reverting characters back to normal once the scene is over.
* DamageReduction:
** What the Defense rating is all about, if in a roundabout way. Since the combat mechanics operate on the principle that damage is part of the same roll as the attack itself, Defense first and foremost decreases the probability of being hit, increasing the number of successes required to land the hit at all. Any surplus still left is turned into damage. So high enough Defence allows you to reduce things like a point-blank burst from a submachine gun to ScratchDamage.
** One of the applications for Style points. For 2 of them, one can ignore 1 point of lethal damage as if it simply didn't happen.
* DashAttack: A character or a creature may make a Charge attack, which involves making a normal move and using a Melee or Brawl attack on an enemy. It offers a handy +2 bonus to the attack itself, but it obviously consumes the Move action that round, and, like most such moves, leaves the character with only a Passive Defense value.
* DeathOfAThousandCuts: Each consecutive attack in the same round applies a -2 debuff to the target's Defense. This means a group of {{Mooks}} can eventually overwhelm the player characters, simply by all of them trying to attack the same person. This also works in the opposite direction - the party can face off against a T. Rex with inadequate weapons, but since everyone is shooting at it, even the weaker attacks can land, simply due to the volume of those attacks.
* DeadManWriting: Supplement ''Mysteries of the Hollow Earth''. The journal of Professor Alexander Trader details his exploration of the Hollow Earth. The journal was found abandoned: Professor Trader's fate is unknown. Near the end of the journal it says:
-->If you are reading this, then all is lost for me, and I most certainly have already shuffled off this mortal coil. My life will not have been in vain, however, if this journal makes it to those who can appreciate my discoveries.
* DeflectorShields: Theurgy magic allows for the creation of all types and shapes of those: directional, spherical bubbles, covering the entire party... even the weakest one provides a substantial +2 Defense rating, but it can go as far as ''+8'', making it all but impossible to land an attack.
* DieselPunk: Downplayed. There are some crazy inventions, but rather than trying to be anachronistic or just building modern machines with [=30s'=] tech, it's instead superscience straight from pulp magazines. It's also relatively rare and always outlandish, rather than commonplace and fully practical.
* DiminishingReturnsForBalance: Third of the Talents that have ranks fall into this category. While they provide useful benefits at higher ranks, they are not as useful as the basic one, while retaining the pricetag. Meanwhile those introduced in expansions [[InvertedTrope go the opposite direction]] - their benefits are squared, rather than linear, causing PowerCreep.
* DrowningMySorrows: One of the example characters, the Psychic Detective, turned to the bottle as a way of dealing with all the voices and being PlaguedByNightmares. He starts with Addiction: Alcohol as a result.
* DrivesLikeCrazy: Any character with sufficiently high Drive or Pilot skill in general, and specifically those that have the Reckless Driver Talent in the ''Secrets of the Surface World'' expansion.
* DualWielding[=/=]GunsAkimbo: Doable, but [[TwoFistedTales given the tone of the game]], gets a SurprisinglyRealisticOutcome - you get high penalty to ''both'' the secondary hand ''and'' the second attack, up to the point where the secondary hand/attack will be completely ineffective, unless having really high Skill Rating. The only way to reduce those penalties is to purchase talent "Dual Wield", but to truly get rid of it, you need to buy '''all three ranks''' of it, for a total of 45 experience, which is an exorbitant price[[note]]It is actually cheaper to just buy 4 ranks of specialisation in given weapon type for 12 experience points, than even a single rank of the related talent, while gaining +4 bonus to ''all'' situations regarding that particular skill, rather than only reducing penalty to DualWielding[[/note]].
* EnemyMine:
** One of the example situations covers a combat scene where a player character yells in German to a group of Thule Society soldiers to band together against lizardmen, followed by a Diplomacy check. While the check fails, the game openly encourages this sort of behaviour and the player is even granted a Style point for quick thinking.
* ExactlyWhatItSaysOnTheTin: To avoid confusion and maintain its trademark speed of gameplay, the game deliberately uses as many obvious and descriptive names for Skills, Talents, and Resources as feasible.
* FlamethrowerBackfire: A person wearing a flamethrower is a potential walking bomb if gunfire hits the flamethrower.
* FoodPills: Nutrient Pills, a possible Artifact Resource in the ''Secrets of the Surface World'' supplement.
* ForScience: One of the most likely motivations for Academics. ''The'' motivation for the [[MadScientist mad variety]].
* FungusHumongous
** Main rules. One of the more exotic surface terrain types in the Hollow Earth is forests of towering mushrooms.
** Supplement ''Mysteries of the Hollow Earth''. Moletown is the underground cave city of the Molemen. The cave that holds the Temple of the Worm has huge forests of phosphorescent fungi, and the fungus farm has fungi that achieve towering heights.
* GanglandDriveBy: The aptly named Talent, Drive-By Attack, not only greatly reduces penalties when firing from a moving vehicle (up to the point of ImprobableAimingSkills), but also offers an option to LeadTheTarget with far better results.
* {{Ghostapo}}: Thule Society, along with few other Nazi organisations, and the Gestapo itself, are all active players in the setting, each in search of [[ArchaeologicalArmsRace the lost Atlantean technology]] or to at least study the magic and occult for practical applications.
* GiantEnemyCrab: supplement ''Mysteries of the Hollow Earth''. The giant crab can grow up to 25 feet long and has [[PowerPincers claws that are six feet long]].
* GiantSpider: One type of monster {{PC}}s can encounter inside the Hollow Earth are giant meat-eating arachnids that are 10 feet long (not including the legs). They hunt like normal spiders, injecting a paralyzing poison with their bite and cocooning the prey to eat later.
* GiantSquid: Kraken are 100 foot long 40 ton squids powerful enough to capsize ships and eat their crews. They can also drag a ship deep underwater and let the pressure and lack of air do their dirty work for them.
* GlassCannon: Magic users, characters either using MoreDakka or meticulous aiming or melee combatants charging their targets all pose to deal a crapload of extra damage... but are only left with their Passive Defense for the duration, being ''greatly'' exposed to counter-attacks and thus even easier to kill.
* GodGuise: Titans sometimes pose as gods in order to receive offerings (food, water etc.) from primitive tribes. They are helped in this trickery by the fact that an adult titan is twice as tall as a human, and an old titan can be as much as thirty feet tall.
* GoneHorriblyWrong: Happens ''twice'' to Thule Society. They realised too late what exactly they did and [[ThoseWackyNazis who]] they put in power, and by the time they've tried to counter the course of action, they were already sidelined. Their grand plan to come back to power was to convince Nazi higher-ups they needed a dedicated, formal organisation for the study of the mysteries of the world and occult powers, ostentiably for the incoming war. Thinking they can subvert it right at the inception, the Society instead ended up locked in an InterserviceRivalry with a freshly minted Ahnenerbe, ''further'' sidelining themselves and access to the resources they were after from the start.
* GoodOldFisticuffs: In the basic ruleset, that's what the Brawl skill was - just punching, in a bar-brawl style. It wasn't until ''Secrets of the Surface World'' expansion that actual Martial Arts were added to the game.
* GoodPaysBetter: The first two ranks of White Magic offer some of the most useful rituals and the rest are not bad, either. Meanwhile, the less ambigious and more straightforward evil BlackMagic gets, the less useful and more risky its spells get.
* GrapplingWithGrapplingRules: This being an Ubiquity game, it's just a single contested check, making it as easy to perform as any other action. What distinguishes grappling is the requirement for a double check from a single roll and against atypical values: first if the grappling happened at all (Brawl vs. ''Size'' of the target, rather than standard Defense) and then if it was successful (remaining "damage" vs. Strength of the target). In practical terms, it means that trying to grapple something big and strong is bound to fail, while smaller and weaker targets are significantly easier to grapple or even pin down. While grappling itself isn't hard to pull or read from dice, when you consider all it does is immobilise the target, there are easier and faster ways to achieve that effect, and ones that aren't so easily countered.
* GreatWhiteHunter: One of the most commonplace archetype for combat-oriented characters, to the point where example character creation is dedicated to making one of those. After all, who else would you expect in a setting where dinos and megafauna are commonplace and far more deadly than any contemporary game?
* HalfHumanHybrid: Atlanteans and humans can - or rather could if Atlanteans were still around - fully interbreed. There are dozens of people who have some trace of Atlantean lineage in them. As a result, they at the very least live longer than regular humans, while often displaying other special properties. Both Terra Arcanum and Thule Society are searching for those, though for completely different purposes. The Grand Masters of the Terra Arcanum are the purest Atlantis lineage accessible at any given moment, allowing them to perform ''Film/{{Highlander}}''-like identity swaps for decades or even centuries - something that the rest of the organisation is unaware of.
* HealingFactor: The game has several versions of this.
** All creatures inside the Hollow Earth heal at twice the normal rate. People have gone to sleep severely injured and woken up completely healed.
** Anyone with the Quick Healer talent heals at twice the normal rate. This benefit is cumulative with the Hollow Earth healing bonus above, for a total benefit of healing at four times the normal rate.
** Lizardmen can regenerate damaged organs and lost limbs. A finger takes a week, an eye or other small organ in two weeks, and a tail, arm or leg in five weeks. This benefit is cumulative with the above examples.
** Inhabitants of Shangri-La heal at four times the rate of the surface world, and anyone who spends a year there will have lost limbs begin to regenerate and birth defects disappear.
* HealingHands: That is literally how the healing spell is named. And it also requires to literally lay hands on the injured area to close the wound and heal any damage done to the body.
* HeroicResolve:
** Whenever the life of character is in danger, they perform a Willpower roll, rather than anything related with their physical stats. In fact, Willpower is even part of equation to determine total Health.
** Diehard is a Talent that makes characters immune to falling unconscious due to their Health reaching 0. More importantly, it allows to shrug off damage that would normally ''kill'' anyone else, while keep going, ''despite having negative Health''.
* HistoricalVillainUpgrade:
** In real life, Thule Society was completely irreverent by 1936 and even prior to that, it was just your regular interwar occult group. Here, it's a genuine cabal of sorcerers who pulled enough clout and strings to ultimately put the Nazis in charge of Germany, for their own personal plans and easy access to national resources.
** The Dominican Order, while somewhat infamous for being "dogs of the pope" and actually meddling in politics in a few instances, is made much more powerful. They are also the foundation for Ordo Spectare and Ordo Umbra, two secret agencies answering only to the Pope.
* HollowWorld: The main setting of the game.
* HornAttack: Creatures that attack with their horns/antlers include the ''Triceratops'', aurochs, "Giant Unicorn" (a huge rhinoceros), Irish Elk (a giant deer) and wooly rhinoceros. The supplement ''Mysteries of the Hollow Earth'' adds the ''Pentaceratops'' and ''Styracosaurus'' (which are similar to ''Triceratops''), the ''Pelorovis'' (similar to the aurochs) and the ''Brontotherium'' (another rhinoceros-like animal), as well as normal (surface world) animals such bulls, deer and rhinoceroses.
* HouseSystem: Ubiquity, a dice pool system based on counting evens.
* HumanSacrifice:
** Since [[BloodMagic magic requires blood]] and quite a lot of it, it's one of the most straightforward ways to gain it, especially if the mage isn't desperate enough to sacrifice their own blood. However, it is ''not'' required to kill anyone. Merely, each lethal wound turns into +2 to Sorcery roll and it can even be done voluntarily, when each party members draws their blood to fuel some important spell in haste. An actual human sacrifice would be an incredibly powerful source of magic, given just how big bonus to Sorcery rating it would generate.
** Supplement ''Mysteries of the Hollow Earth''. The Sun God priests in the city of El Dorado cut the hearts out of sacrifices with a razor sharp quartz knife, then hold them up [[BeatStillMyHeart while they're still beating]].
* ImAHumanitarian: Supplement ''Mysteries of the Hollow Earth''. Cannibals hunt, kill and eat human beings. Molemen will capture and eat humans who intrude into Moletown and those who encounter their hunting parties on the surface.
* ImprobableAimingSkills: A combination of various Talents, specialisation in a given weapon type and sheer Skill rating allow one to pull off impossible shots. ''Then'' there are also trick shots involving ricochets and similar.
* ImprovisedBandage: They cause a -2 penalty to the Medicine roll, but you still need to use ''something'' to patch the wounds in the first place, making them better than not being able to perform the action at all.
* IslandBase: If a character has the Resource of Refuge 5 they have a secret island base with everything they could want.
* JackOfAllTrades: The Jack of All Trades Talent in the ''Secrets of the Surface World'' supplement.
* JetPack: This is an Artifact Resource in the main rules and the ''Secrets of the Surface World'' supplement. It has a speed of 100 m.p.h. If the wearer carries another person, top speed is cut in half and maneuverability is reduced.
* JumpingOffTheSlipperySlope: Necromancy as a whole. Tier 1 spell? A ritual to summon a spirit and make a regular seance with it - and the spirits actually ''like'' those, being finally able to communicate with the living. Tier 5? Tearing a hole in the fabric of the Universe and summoning an EldritchAbomination - ''without'' a guarantee it's going to be docile.
* KillItWithFire: Subverted. Warmth wakes up Antarctic horrors.
* KingInTheMountain: At least on Mars, the Atlanteans entered a kind of hibernation. Their physical bodies are sleeping in hidden places. But they can still manifest physical avatars that contain a fraction of their power, to effect the world.
* LadyLand: Amazons society operates as a StrawFeminist matriarchy. They have ''very'' low opinion on men and consider them not worth doing anything else than tending the kitchen. And no, none of them [[AllAmazonsWantHercules wants a Hercules]]. ''Mysteries of the Hollow Earth'' openly mentions they pacify menfolk with brutal means whenever they get the uppity to demand something else than their traditional role.
* TheLastOfTheseIsNotLikeTheOthers: Necromancy includes things like TalkingToTheDead, casting curses, [[LifeDrain draining life force]], AnimateDead... and summoning {{Eldritch Abomination}}s of all shapes and sizes.
* ALighterShadeOfBlack: The Fifth Columnists, the secret organisation of "German patriots" within the Thule Society. In other words - the "good" Nazis fighting against a cabal of evil, power-hungry sorcerors, for the betterment of Germany and its true destiny.
* LifeDrain: One of the ''less'' nasty things Necromancy can do to people.
* LostWorld: Dinosaurs and other prehistoric beasts, such as Cenozoic mammals and giant Paleozoic arthropods, abound in the Hollow Earth.
* LuckManipulationMechanic: Subverted. Style points allow to add extra dice to a specific roll, but that doesn't affect the outcome itself (you can still roll even a CriticalFailure). Similarly, chance dice allow to roll more, but at an increased penalty, balancing any gain achieved this way and simply making it a gamble. Chance dice, on the other hand, allow you to roll normally impossible check: even if it fails, it can still potentially cause less harm than a roll that is outright impossible to make.
* LuckilyMyShieldWillProtectMe: Downplayed. Shields do provide a bit of Passive Defense and as such, make it harder to be hit by any sort of attack. However, that value is rather low and is only worth it when paired with a decent armour.
* MacGyvering: The incredibly useful Talent, Jury Rig, allows to perform repairs without having access to spare parts. And it has three ranks, offering a +4 to Repair check when maxed out. This can be further combined with Tinker Talent, removing penalties for lack of proper tools, too.
* MadScientist: The game explicitly differs between regular Academics doing research and obsessive Scientists that try to "prove something". And then are those various eggheads who GoMadFromTheRevelation.
* MagicAIsMagicA: While magic powers are purposefully vaguely described and classified, using spells from the "wrong" school than the one the character knows results in a -2 penalty, as if making an unskilled roll.
* MagicVersusScience: Heavily downplayed. TThe only example is Medicine roll causing penalty to applying HealingHands - but only because the shock has been stabilised using medical skills, rather than magic powers.
* MagicalGesture: Implied. Whenever they are unable to make them, characters suffer a debilitating -4 penalty to Sorcery (which can go as far as nullifying their entire Skill rating).
* MamaBear: Main rules sample adventure. When the {{PC}}s first arrive in the Hollow Earth they will encounter a herd of ''Triceratops'', including a mother and her child. If the {{PC}}s get too close the mother will charge them, and if they attack the child she will become enraged.
* TheManBehindTheMan: Initiates and the first tier of agents of Terra Arcanum are clueless puppets... and so are the Overseers from the upper tier that are manipulating them. The whole organisation actively dupes its own people for the ultimate goal of keeping the existence of the Hollow Earth and Atlantis secret, even from its own ranks.
* TheManMakesTheWeapon: One of the core rules of the whole game and what allows all sort of characters shine. Weapons have pre-definied values to them, which only go so far. And for non-specialists, if given equipment comes with low value, it will remain so. But a dedicated [[TheGunslinger gunslinger]] can easily kill someone with a tiny derringer from improbable range, while a WarriorMonk will perform InstantDeathStab with a throwing knife - ''despite'' both of those weapons being near-useless for everyone else. This further extends to variety of Talents, which allow to swap stats used for Skill rating, weaponizing high Intelligence, Willpower or Charisma for characters with lackluster physical stats, which in turn removes the typical issue various [=RPGs=] have with skill monkeys and party faces characters.
* {{UsefulNotes/Mars}}: The main setting the for the PlanetaryRomance sourcebook, ''Revelations of Mars''.
* {{Megalodon}}: One of the most dangerous predators in the seas of the Hollow Earth is the megalodon, a shark that's more than 100 feet long and weighs more than 50 tons. They feed on whales and plesiosaurs, but avoid attacking the [[GiantSquid kraken]].
* MeleeDisarming: Any given character can be disarmed with one of the basic Brawl and Melee moves. At mere -2 attack debuff, it is possible to either knock the weapon out of reach, or, in the case of Brawl, ''even steal it'' and brandish it right back at the target.
* TheMenInBlack: The Paranormal Investigator archetype in the ''Secrets of the Surface World'' supplement.
* MightyGlacier: Total Defense. You can't attack and you can barely move around, but your Defense is increased by +4. To put that into perspective - that's equal to wearing a suit of PoweredArmor or sitting in a foxhole.
* MonowheelMayhem: The Wheelbike in the Weird Science chapter of the ''Secrets of the Surface World'' supplement.
* MoreDakka: Automatic weapons gain +1 bonus during Burst (3 rounds) and +3 in Autofire bonus to hitting the target. It's less about aiming and more about simply ''saturating the area with bullets''. Straffing Fire takes it a step further by not only applying an Autofire bonus but also allowing you to hit multiple targets in a single attack if they are close enough. The main downside of automatic weapons is how many bullets they use for those sorts of attacks and how uneconomic they are in the long run, which might be a problem when stuck inside the Hollow Earth.
* MyKungFuIsStrongerThanYours: Optional rules for Martial Arts specifically list this sort of attitude, specifically for kung-fu: one training just to best a very specific opponent and their style of fighting.
* MysteriousAntarctica:
** One of easiest ways of getting beneth the surface is using one of the polar shafts and a ''lot'' of weird things is going on surface of Earth around both poles thanks to said shafts.
** Played straight with Frozen City of Terror, which is a ruin of an Atlantean City, infested by their old bio-weapon experiment. The only thing keeping it safe is the freezing temperature, but a German expedition send there started to thaw the ice...
* NobleSavage: Supplement ''Mysteries of the Hollow Earth''. There are entire tribes of this character type in the Hollow Earth. They are regal and wise, respecting nature and trying to maintain the ecological balance of the area where they live.