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