What would a game be without some adversaries to stand between you and your goals? Dark Forces has Imperials, bouty hunters, strange and exotic animals and droids whose sole objective is your destruction. So you'll want to be smart and read up on them here before heading out on your missions.
A lot of this information is from common knowledge on Star Wars, some comes from hearsay and some of it is off the top of my head. If I made a blatant error with the information let me know so I can correct it. But it should be pretty accurate. The shot table at the bottom was compiled by Paulius Stepanas and is courtesy of the Dark Forces FAQList.