Here is the full list of all 23 Chainsaw Warrior achievements.
Kill 2000 enemies in combat
Kill 50 Mutants in combat
Kill Darkness 25 times on any difficulty
Kill the Meat Machine 25 times in combat
Kill 1000 monsters in combat
Take 100 points of venom damage
Kill 100 Agents in combat
Kill 10 Slimes in combat
Take 250 points of radiation damage
Kill 50 Rats in combat
Discover all 9 Outcomes
Use items to bypass 50 traps
Kill 200 Zombies in combat
Punch Darkness... Right in the face
Take 200 points of physical damage
Beat the game on Medium setting
Beat the game on Easy setting
Beat the game on Hard setting