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