Former Soldiers:
They resemble your old friends, but now they just fire pistols at you. They drop clips for the chaingun and pistol when killed.

Former Sergeants:
Meaner and tougher. They carry shotguns and do more damage then soldiers. They drop shotguns when killed.

Imp:
This creature throws fireballs and takes more bullets to kill.

Demon:
Appear in most areas and can rip your head off if you are not careful. If you see more of them, use the chaingun.

Cacodemon:
These creatures are ugly and have one big mouth. If they see you, they will fire lightning balls from their mouth. Use your rockets.

Mancubus:
You have to use more then a chaingun to kill them. Use ammo with caution.

Arachnotron:
Fires plasma energy at you. Use your rifle.

Spider Demon:
The ultimate enemy. Has a super chaingun mounted on her body. Use your plasma rifle or rocket launcher.