Notes

Chemicals to make a deadliest npc:
Blockshield (5x)
Superspeed
Face
SCP-096
CrazyX
Toilet (Decorative)
Chainsaw
FlameX
TimeSkip
Blast
Attack
Orbits

for experimentation:
Compatibility criteria:
NC - Not Compatible
SC - Slightly Compatible
C - Compatible

Result of virus testing for the deadliest npc:

First Group:
Funny Viruses:
Wrench - NC (only made the entire body wrench)
Attack - C (the cooldown is slightly slow)
Bomber - NC (Only used one bomb, nothing else.)
Face - C (makes an armor, possibly be combined with blockshield)
Freezenella - NC (it's useless, it only turns the npc into ice, although alteranating..)

Bio Weapon Viruses
ROXX-3 - SC (it just follows you around, also glitching your body)
EyeHurt - C (blinds the person)
CrazyX - SC (Ragdolls you)
ZomboidX90 - C (Damages you when it touches you)
SCP-096 - C (Runs Fast, Increased HP to 300)

Hazard Viruses:
Gogo - NC (dude just sprays a circle thing at the other direction, wtf)
Bubble-1 - NC (Became corrupted)
Splash-X - SC (Splashes balls that slightly damages the player)
FlameX - C (Sets you on fire, damaging you rapidly)

2nd Group:
Strange Viruses:
Chainsaw - SC (same thing as zomboid, except you get damage from the chainsaw blades)
Blockshield - C (impenetrable, only weakness is the visible parts)
SuperSpeed - C (increases speed, making it fast as if you we're sprinting)
Tall - C (if combined with 2 shots of blockshield, although slightly harder to inject the virus into the subject)
Toilet - NC (only used for decoration)

Crazy Viruses:
Mutantoisis - NC (only makes extra heads and limbs)
Spinox - NC (Only spins the subject, expands the head)
Exon - NC (has stringy arms, damages itself by 5)
Epical - NC (inflates for 6 seconds, before deflating, and inflating again..)
Brick - NC (a wall that doesn't protect the subject from damage..)

New Viruses:
TimeSkip (aka TimeStop) - SC (Punches you with no damage, could be useful when killing players.)
RingAura - SC (Releases a ring aura, temporarily stunning the player)
Blast - C (Makes an explosion blast, damages the player's hp significantly.)
Side Effect: Takes the NPC's Health by the number of 5
Rocket.exe - NC (Although deals a significant damage, players could dodge the rocket.)
Orbit - SC (Deals a little damage, could be used for defense against melee players.)