Here is the full list of all 15 The Mooseman achievements.
We too have a cow level
Solve the ice crystal riddle in the underworld
Find all the artefacts among Mangonth's tusks
Fight and defeat the spider of the Lower World
Escape the river god
Solve the riddle of Vorsa's sanctuary
Enter the world of men
Outsmart Yoma the Witch
Enter the world of gods and ancestors
Survive the chase by Voipel
Return to the gates of the Lower World
Collect all artefacts
Grab a piece of shimmering sun
Enter the world of the dead and ancient spirits
Outsmart the guardian of the Lower World