This book is arranged from the least lethal to the most lethal. This was put together by personal accounts of the survivors.
Undead - The dead resurrected through the
bites of the other dead through inhaling the poisons gas near the crack(s) that opened across the country. They're slow and show no sign of intelligence or memories of past life. Kill by destroying the brain or separating the head.
Ghouls - Souls of the damned manifested in a physical form. They crawl from the cracks, and hunt during the day and night. They're as fast as an average human though generally stronger than. To kill these Ghouls you have to destroy their body or to burn them.
Muties - People who were not killed by the initial contact with toxic gas, it causes them to warp and mutate. They're intelligent enough to set up basic traps and use simple tools. They can die by blood loss, main organ damage, or destruction of the body.
Witches - Damned harpies from the underworld who can tamper with the mind of the living causing them to hallucinate and attack friend or foes alike. Witches can't cross running water, so if you're being chased run as fast as you can and get over a bridge. They can be killed with fire or drowning.
Vampires - These are not people, they look like the people you used to know but they're not. They capture their victims and drain their blood over the course of a few weeks. The longer the beast has been with out blood the more obvious it is. You have to put a stake through its heart, burn it then remove its head. These are very dangerous be careful.
Lesser Demons - These are one of the top hunters, they move in packs and have an unsaitable appetite for the flesh of the living. If you come across the these run, their bodies can take mass damage, and if not completely destroyed or incapacitated they can return. They've been known to hunt prey for hundreds of miles.
Wraiths - They were once the souls of the tormented raised up from the depths of hell they haunt places of evil. Frequenting mass graves and other places of similar atrocities. They can only be killed during the day light hours, during this time normal means can kill them. They're rare to find during the day as they lay dormant in the bodies of the dead. If they touch you, they will leach you of your life essence.
Fiend - These beasts can't be killed by ordinary means, holy water slows them, and they can't cross holy ground. Very little places are safe from these creatures. They feed off the anguish of mortals and they frequently drain people of their life essence. They latch onto prey and are hard to discover until the person dies.
Greater Demons - Few have ever seen them, and fewer have lived to tell tales. If you run into one there is no escape. Those who have lived are changed forever and don't live long after. God help you.