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