Here is the full list of all 30 Sons of Valhalla achievements.
Tutorial finished
Valgard defeated
Bishop defeated
Bloodhound defeated
Sir William defeated
Loki defeated
Escaped Niflheim
Scarecrow defeated
Fire devil defeated
Fur trader defeated
Priest master defeated
Graveyard keeper defeated
Tribal leader defeated
Slave trader defeated
Butcher defeated
Little man defeated
Quarry giant defeated
Trainer defeated
Crocodile hunter defeated
Knight defeated
Sailor defeated
Raya escaped
Thorald and Raya reunited
Man's best friend
Defeated wave 25 in Horde mode
Defeated wave 35 in Horde mode
Defeated wave 45 in Horde mode
Defeated wave 55 in Horde mode
Defeated wave 65 in Horde mode
Defeated wave 75 in Horde mode