Here is the full list of all 20 Völgarr the Viking achievements.
Obtain a Warrior Spirit
Block a projectile with the shield while in the air
Block an attack with the shield while on a rope/chain
Wield the fire sword
Unlock Mjolnir's power
Defeat the Lizardmen King
Break the Magic Seal on Fafnir's Tower
Complete the game and earn Ending C
Complete the game and earn Ending B
Complete the game and earn Ending A
Kill 4 enemies with a single charged spear attack
Hitch a ride on a spear attached to an enemy shield
Collect a golden walrus statue
Reach the alternate path for any world
Find a Key Stone
Kill Fafnir before he reaches his Dragon form
Reach Yggdrasil's roots
Complete any world without ever losing any equipment
Complete any world in 4 minutes or less
Complete the game with 10 or less retries (deaths)