So, erm, here's a monsters-only version of Weasel Presents: Nazis v2.
I scrubbed it of player and weapon stuff, so it's just the monsters, sounds, and so on. Because Nazis v2 has certain enemy properties that depend on difficulty choice (specifically, its own custom difficulty settings), I added a setting in Options that allows you to scale the damage and speed of enemy projectiles (it really just tells the mod whether to use, say, an easy-difficulty projectile or a hard-difficulty projectile, for example, as they are predefined) and tried to emulate the increased aggressiveness of the higher difficulties (the Tracer Damage setting also regulates this).
EDIT: I updated it with an extra CVAR, which allows you to change the Demon replacements to Spectre replacements (only relevant because the Demon replacements in Nazis v2 are attack dogs, and shooting dogs - even Nazi dogs - just feels bad whenever I play. Shooting Paratroopers and Nazi Mutants instead seems more palatable).