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