Here is the full list of all 18 Munin achievements.
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Complete Ālfheimr
Complete Svártalfheimr
Complete Múspellsheimr
Complete Vanaheimr
Light up 4 Runes at the same time
Complete Helgardhr
Free 9 Orb spirits
Complete Nifleheimr
Collect 9 Feathers while underwater
Complete Jötunheimr
Complete Midgardr
Stand on top a rolling boulder for more than 3 seconds
Finish the last level in 45 seconds or less
Complete Ásgarð
Die in all the different ways possible
Collect 999 Feathers
Finish 9 levels without jumping