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