Here is the full list of all 31 The Bug Butcher achievements.
Kill 1000 enemies with the gatling gun in any single game mode
Complete 15 rounds without dying
Kill 1000 enemies with the chain lightning gun in any single game mode
Kill 1000 enemies with the rocket launcher in any single game mode
Collect 3 stars on every level of floor 5!
Kill 1000 enemies with the laser beam in any single game mode
Beat the target Combo for all levels on floor 05!
Kill 1000 frozen enemies in any single game mode
Unlock all perks in arcade mode
Beat the target Combo for all levels on floor 04!
Collect 3 stars on every level of floor 4!
Unlock all powerups in arcade mode
Survive 60 seconds wihout shooting on level 22 in HARD
Don't let the spider touch a scientist on level 21
Unlock all weapons in arcade mode
Don't use any powerup in level 18
Dash into a frozen face hugger enemie on the ground
Don't use any powerup in level 12
Don't let the spider touch a scientist on level 10
Survive 30 seconds without shooting on level 9 in HARD
Don't let the spider touch a scientist on level 8
Don't use any powerup in level 6
Survive 45 seconds without shooting on level 6 in HARD
Kill 1000 enemies with machine gun in any single game mode
Collect 3 stars on every level of floor 3!
Beat the target Combo for all levels on floor 03!
Collect 3 stars on every level of floor 2!
Beat the target Combo for all levels on floor 02!
Collect 3 stars on every level of floor 1!
Beat the target Combo for all levels on floor 01!
Complete 5 rounds without dying