Here is the full list of all 20 Wildcat Gun Machine achievements.
upgrade to 2 respawn cats
find a special weapon
purchase all movement speed upgrades
purchase all dash upgrades
purchase all grenade upgrades
upgrade to 9 respawn cats
purchase all pistols
acquire all weapons in the game
dash 20 times before triggering the cooldown
defeat meat sack
defeat spawning queen
defeat rot belcher
defeat sluggoth
defeat unthinkable horror
unspeakable horror
defeat votolato, heart of the beast
defeat serbian, mind of the beast
defeat zinnerblilie, eye of the beast
defeat the remnants
defeat nosraep, true form of the beast