Feigning death means the npc has a chance to revive after dying
Serrated claws means an npc's attack can inflict a bleed effect

Shambler - Normal zombie, durable and hard to keep down if not shot in the head.
Can feign death.

Flayed Zombie - A shambler that has survived a gruesome accident. With its flesh mangled and warped; it has longer, serrated claws.
Can feign death.

Feral Shambler - A Shambler with a mutation identical to a Prowler's, it is strong as its normal counterpart, while still being extremely agile.
Cannot feign death.

Fresh Dead - Human recently turned into a zombie, fast and weak. Should it feign death, it turns into a normal Shambler.
Can feign death.

Prowler - A boney cadaver with extreme dexterity, speed, and persistence. Although weak, it is very strong in numbers.
Can feign death.

Gangrenous Zombie - A rotting, bloated zombie covered head to toe in a thick, viscous blood that acts as a coat of weak armor, it has long claws and is very beefy.
Can feign death.

Bloat - A poisonous zombie with a massive build, it is very strong and can take a large beating.
Cannot feign death.

Thrall - A Bloat with a fleshy, mutilated, and disfigured appearance due to the damage it has taken and surroundings it adapted to.
It has long claws which are serrated.
Its body can also take a lot of damage before dying.
Cannot feign death.

Putrid Zombie - A Bloat with its skin flayed, revealing the disgusting, poisonous muscle layer and flesh.
It also has the ability to toss its own acidic flesh to wherever it desires.
Cannot feign death

Aggressor - A Zombine that has mutated in a way similar to a prowler.
keeps its armor and strength and gains inhuman agility
Can feign death.

Chimera - A Zombine which has suffered the same accident as a Flayed Zombie's, with its flesh burned and warped.
It, however, has more health unlike a normal Flayed Zombie.
Cannot feign death.

Zombine - A Combine Soldier that has been zombified.
With its beaten Overwatch Standard Issue Combat Armor still on, it has a high resistance to gunfire and melee.
Can feign death.

Frigid Revenant - A Revenant chilled to the bone, it can freeze things with only its touch, making something slow down on attack, dangerous in groups.
Can feign death.

Revenant - A skeletal zombie which has developed a small resistance to gunfire and melee, its attacks are weak, its moderately high HP makes up for this.
Can feign death.

Starved - A malnourished zombie, yearning for any amount of flesh to get its hands on.
Although weak like the Prowlers, they are strong in numbers.
Cannot feign death.

Ghoul - A fragile and weaker, but extremely poisonous zombie that can toss its own acidic flesh.
It can debilitate humans with only a single swipe of its claw, capable enough of reducing a sprint down to a crawl.
Can feign death.

Withered Ghoul - A Ghoul that has aged with time, and has been malnourished, it as adapted to many conditions and can take more abuse, and has longer, serrated claws. Its debilitating slow is just as potent and dangerous.
Can feign death.

Alpha Ghoul - A Ghoul that has evolved to a point where it is as agile as a prowler. Its slowing attack is much less potent.
Can feign death.

Chilled Ghoul - A frostbitten Ghoul that has exchanged a debilitating poison for a freezing attack with a slow just as powerful.
Its body has developed a crystalline layer of ice around its body that acts as weak armor.
It also has the ability to throw goops of frozen acid where it desires.
Can feign death.