This adds an debug menu which give you the ability to change any monster, weapon, item, decoration, dead thing, and key to any others that are similar to it. So you instead of a zombieman, you can choose to have an cyberdemon in that monster's place for example.
I was going to make this just as close to Doom 2 as possible, but decided to also add all of the ZDoom extras within the menu. The menu has stealth variations of all monsters, dead bodies of most monsters, and three extra weapons with one of them including the beta version of the BFG 9000, and the Doom beta score items that were eventually scrapped from the final product.
