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