Here is the full list of all 18 Munin achievements.
Complete Svártalfheimr
Watch the whole credits at normal speed from the Chapters Menu
Die in all the different ways possible
Collect 999 Feathers
Complete Ālfheimr
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
Finish 9 levels without jumping
Stand on top a rolling boulder for more than 3 seconds
Complete Midgardr
Finish the last level in 45 seconds or less
Complete Ásgarð