Here is the full list of all 15 Tyrfing Cycle achievements.
Restore your earthly form
Pull of a quick Counter
Kill Mimir
Kill Evney
Kill Skoll
Defeat Hela
Find all of the secrets in a Helheim run
Kill the corpse plant
Kill 100 monsters
Earn an A rank on Helheim
Kill 50 monsters
Hit Evney even when she is dead
Create Black Flames
Use lightning Release to kill bugs, duh
Complete the Rune Challenge in Helheim