Here is the full list of all 49 Muck achievements.
Kill 10,000 mobs
Beat the game without any players picking up a powerup
Beat the game alone without taking any damage (Normal difficulty or harder)
Beat the game using only a rock as your weapon / tool. This goes for all players.
Die 100 Times
Beat the game with 2 players, but no one can take any damage (Normal diff or harder)
Survive for 100 days
Swim 25km
Collect all 5 gems
Jump 10,000 times
Slay 1000 goblins
Kill 200 enemies using bows
Build 250 builds
Die 50 Times
Pick up 10 Milk powerups in one game
Kill 250 cows
Start 200 battle totems
Open Chiefs chest
Beat the game on gamer difficulty
Beat the game in less than 10 days on Gamer mode
Beat the game on normal difficulty
Beat the game in less than 8 days
Wield the Night Blade
Open 500 chests
Find and wishlist Karlson in Muck
Kill 1,000 mobs
Craft 1,000 coins
Die 25 times
Kill a friend on Survival Mode
Drown
Beat the game on easy difficulty
Leave Muck
Defeat Guardian
Slay all bosses
Die 10 times
Eat 50 red shrooms without growing bigger
Defeat Gronk
Defeat Chief
Defeat big chunk
Kill 100 mobs
Revive a teammate
Play Muck for the first time
Beat the game with 4 players, but no one can take any damage (Normal diff or harder)
Beat the game with 8 players, but no one can take any damage (Normal diff or harder)
Kill 100,000 mobs
Kill 250 buff mobs
Walk 250km
Beat the game using only a rock, taking no damage and using no powerups. This goes for all players in lobby. (Normal or harder)