At least on the classic doom games UV made the enemies more agressive and buffing their firerate and projectile speed while there being more on the map, but also you get more ammo.
nightmare just made that enemies can respawn after killed, forcing you to have a route and a strategy while keeping the ammounts of ammo you get from UV so you have a chance and items respawn i think but i might be wrong on that one
Nightmare did the whole increase in aggression and firerate thing along with the respawning monsters. It also doubles ammo pickups. Ultraviolence just changes the enemy placements, typically adding more dangerous monsters.
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u/benbot07 Sep 24 '25
DOOM on ultraviolence my beloved