Here is the full list of all 28 Gorescript achievements.
Finish the first level.
Finish a level in less than 3 minutes.
Perform a jump kill.
Find all the random powerups in the first level.
Finish a level in less than 1 minute.
Finish all the levels in less than 3 minutes each.
Finish all the levels in less than 1 minute each.
Get all the weapons.
Get all the artifacts.
Find all the random powerups across all levels.
Beat the first boss.
Beat the second boss and finish the game.
Finish the game on Masochistic difficulty.
Finish the game on Blackout mode.
Finish the game on Permadeath mode.
Finish the game on Masochistic Blackout Permadeath mode.
Get the random powerup in the "Why?" room.
Damage 6 enemies with one railgun shot.
Damage 6 enemies with one rocket.
Using only the Sledgehammer, kill at least 50 enemies in a level and finish it.
Using only the Double Shotgun, kill at least 50 enemies in a level and finish it.
Using only the HyperBlaster, kill at least 50 enemies in a level and finish it.
Using only the Holy Rocket Launcher, kill at least 50 enemies in a level and finish it.
Using only the Railgun, kill at least 50 enemies in a level and finish it.
Using only the "Killer" Anti-Grav Boots, kill at least 50 enemies in a level and finish it.
Finish a level without killing any enemy yourself (shield reflect kills included).
Get the random powerup at the end of the strafe running challenge in the Causeway level.
Beat the final boss without taking any damage yourself.