Here is the full list of all 49 Muck achievements.
Beat the game on easy difficulty
Leave Muck
Defeat Chief
Defeat Guardian
Defeat Gronk
Die 10 times
Kill 100 mobs
Open Chiefs chest
Play Muck for the first time
Beat the game on normal 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 1,000 mobs
Kill 10,000 mobs
Kill 100,000 mobs
Kill 250 buff mobs
Kill 200 enemies using bows
Kill 250 cows
Defeat big chunk
Slay all bosses
Start 200 battle totems
Slay 1000 goblins
Die 25 times
Die 50 Times
Die 100 Times
Drown
Open 500 chests
Build 250 builds
Craft 1,000 coins
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
Find and wishlist Karlson in Muck
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)