An Old Memory

Obviously, the ordinary zombies are Level 1, Hunters are Level 2, Strikers who are great at sneak attacking are Level 3, while like a Kabutops, super rare pokemon, Screamers are Level 4, and there's the regular Tanker at Level 5, and last but not the least, with a Danger Level of Six, the Z, it might be physically weak compared to the other zombies, but it's ability to control zombies and create a horde makes it the most dangerous and troublesome opponent.

As one survivor had once quoted,

"I'd rather face a Tanker alone, than to face a Z and suffer its horde of monsters"

Sadly, that survivor had already disappeared from the face of the planet, but his words will certainly not be forgotten and will be passed on to the future generations.

On the other hand, mutated animals only had two distinctions.