Here is the full list of all 22 Morkredd achievements.
Start a co-op game
Squish all the worms
Get killed by a shadow
Complete the game alone
Complete the game with a friend
Complete The Prologue without dying
Complete The Sewer without dying
Complete The River without dying
Complete The Mountain without dying
Complete The Temple without dying
Complete The End without dying
Complete the whole game without dying
Finish the game within 120 minutes
Disturb all the legs
Make noise with all the wind chimes
Pop 50 pimples in The Meat
Find a mural in The Sewer
Find a mural in The River
Find a mural in The Mountain
Find a mural in The Temple
Find a mural in The Meat
Find all the discoveries