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