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