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