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