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