Fast monsters
From Doom Wiki
Fast monsters is a setting which makes monsters more aggressive.
The more common demonic monsters form the original Doom are the most affected by this mode. Demons and the related spectres move and attack twice as fast than usual. Some projectiles are sped up to 15 units per tic, making imp and cacodemon fireballs 50% faster than usual, while hell knight and baron of hell projectiles are 33% faster. These and other monsters also attack very often, shooting and moving very little as long as they have their target in sight, which makes hitscan enemies considerably more dangerous, and the player's fist and chainsaw much less useful.
Fast monsters show up by default only on Nightmare mode.
The setting can be used with any skill level using the -fast command line argument.
