Here is the full list of all 83 Slime 3K: Rise Against Despot achievements.
Kill 999 Black Swordsmen
Unlock every achievement!
Get a level 3 copy of Triangle of Darkness
Kill 6000 Specters
Unlock every ability
Kill 10000 Bees
Get a level 3 copy of Obedient Doc
Get a level 3 copy of Meteorite Satellites
Get a level 3 copy of Super Scytherang
Kill 30000 Tomatoes
Get a level 3 copy of Fiery Horizon
Get a level 3 copy of Supreme Gun
Get a level 3 copy of Homing Loogie
Kill 3000 Brains
Get a level 3 copy of Caliperang
Beat level 10
Unlock all Slime starting setups
Beat level 9
Kill 10 Thornies
Get a level 3 copy of Olive Gun
Beat level 7
Beat level 8
Beat level 6
Get a level 3 copy of Coin Launcher
Beat level 5
Get a level 3 copy of Tiny Spring
Get a level 3 copy of Disco
Get a level 3 copy of "Heretic's Fork"
Kill 5000 Doc Ocs
Get a level 3 copy of Candy Bomb
Kill 2000 Martial Arts Masters
Kill 3000 Ballerinas
Kill 100000 Newbies
Kill 300 Bots
Kill 300 Mantraps
Get a level 3 copy of Blaster
Get a level 3 copy of Bananarang
Get a level 3 copy of Dark Side
Kill 666 Maniacs
Beat level 4
Kill 1000 Stilt-Walkers
Get a level 3 copy of Fire Beam
Get a level 3 copy of Nuggets of Darkness
Get a level 3 copy of Needle Shotgun
Kill 300 Pain Lovers
Get a level 3 copy of Money Box
Get a level 3 copy of Rocket Launcher
Get a level 3 copy of Shotgun
Get a level 3 copy of Watermelon Launcher
Get a level 3 copy of Scytherang
Get a level 3 copy of Random Nails
Get a level 3 copy of Supreme Shotgun
Get a level 3 copy of Flashes
Get a level 3 copy of Obedient Zombie
Kill 200 Shieldbearers
Get a level 3 copy of Assault Rifle
Kill 600 Laser Swordsmen
Kill 666 Fire Mages
Beat level 3
Kill 50 Fridge Men
Kill 1 Wheelman
Get a level 3 copy of Pistol
Beat level 2
Kill 2 Watchers
Kill 10 Madmen
Beat level 1