DOOM + DOOM II

Legacy of Rust contains new enemies not found in the original Dooms 1 & 2.

The new enemies are:
Banshee - floating screaming red blob with a face
Ghoul - based off an early Lost Soul design
Shocktrooper - looks like the player model
Mindweaver - based off an early Arachnotron design
Vassago - large black demon that shoots fire
Tyrant - green variant of Cyberdemon

(all levels are in Legacy of Rust)
There are Banshees and Ghouls right at the start of E2M5. Shocktroopers can be found in E1M0 Ash Mill behind the big windmill. Mindweavers are the first enemies you'll encounter on E1M6. E2M7 contains both Vassago and Tyrants. Use noclip to find all these enemies more quickly.

The original enemies:
Zombieman, Shotgun Guy, Imp, Demon, Spectre, Baron of Hell, Cacodemon, Lost Soul, Spiderdemon, Heavy Weapon Dude, Hell Knight, Revenant, Mancubus, Arachnotron, Pain Elemental, Arch-Vile, Cyberdemon

The easter egg enemies (Wolfenstein SS, Commander Keen, and the final boss head) aren't needed.

There are 23 enemies to kill. Apart from all the enemies you expect in DOOM and DOOM II, Legacy of Rust also bring several new enemies. You'll fight some on the last stage (E2M7); E2M5 is a handy place to get the Banshee enemy, which I was struggling to find as my last one.