Here is the full list of all 80 Rise of the Triad achievements.
Beat the Game on Medium Difficulty
Beat the Game on Hard Difficulty
Beat the Game on Ludicrous difficulty
Kill 666 Enemies with the Heat Seeker
Complete E4L4 100%
Complete Episode 4 100%
Kill 666 Enemies with the Split Missile
Complete E4L3 100%
Find the Dopefish
Kill 666 Enemies with the Firebomb
Complete E4L2 100%
Kill 666 Enemies with the Flamewall
Complete E4L1 100%
Kill 666 Enemies with the Excalibat
Kill 666 Enemies While in God Mode
Kill 666 Enemies with the Drunk Missile
Complete E3L5 100%
Kill 666 Enemies with the Doomstick
Complete Episode 3 100%
Complete E3L4 100%
Complete E3L3 100%
Complete E3L2 100%
Complete E3L1 100%
Complete E2L5 100%
Complete E2L4 100%
Complete Episode 2 100%
Complete E2L3 100%
Kill 666 Enemies with Knives
Kill 666 Enemies with the Rocket Launcher
Complete E2L2 100%
Find Scott's Mystical Head
Complete E2L1 100%
Complete E1L5 100%
Complete E1L4 100%
Complete Episode 1 100%
Complete E1L3 100%
Complete E1L2 100%
Complete E1L1 100%
Kill 666 Enemies with Pistols
Play Through All The Secret Levels
Get 2000000 Points in One Level
Kill 666 Enemies with the Dark Staff
Get "Ludicrous gibs" With All Weapons that are Capable of Gibbing
Eat 4 Health Pickups While in Shrooms Mode
Kill 666 Enemies While in Dog Mode
Eat 3 Porridge Bowls in 5 Seconds
Kill 3 Enemies at Once with the Barkblast
Beat General Darian in 3 Minutes
Kill 666 Enemies with the MP40
Disable Gore
Complete E4L5 100%
Complete Episode 4
Beat the Game on Easy Difficulty
Finish the Game in 4 Hours or Less
Beat El Oscuro in 3 Minutes
Get the Bad Ending
Complete Episode 3
Beat NME in 5 Minutes
Kill an Enemy During a Rocket Jump
Complete Episode 2
Beat Krist in 3 Minutes
Kill 50 Enemies by Using Their Own Traps Against Them
Kill an Enforcer with a Single Pistol
Activate the Original Soundtrack
Complete Episode 1
Gib 2 Enemies with the Split Missile
Eat 50 Meals
Get Shrooms Mode for the First Time
Run the Game on Maximum Ludicrous Settings
Kill 5 People at Once with Explosives or Magical Weapons
Kill 3 Different Types of Triads with One Attack
Kill an Enemy While Under the Effects of a Jump Pad
Submit a Score to the Leaderboard
Collect 10 Coins in 5 Seconds
Gib 50 Enemies
Pick up the Doomstick for the first time
Kill an Enemy with an Exploding Barrel
Get Killed by an Enemy Who Was Previously Begging for His Life
Kill an Enemy While He's Begging for His Life
Run the Game with a Custom Mod or Map Installed