Here is the full list of all 12 SolSeraph achievements.
Make sure the bonfire is not hit for 7 consecutive enemy waves.
Defeat 300 enemies while building a town.
Strike down the King of Trees.
Strike down the Queen of Ice.
Strike down the King of Fire.
Strike down the King of Floods.
Strike down the Queen of Bones.
Defeat the Knight of Dusk.
Defeat the manifestation of Chaos.
Use all of the sun god's special abilities while in knight form.
Complete a combat level without being damaged.
Lead your people to build a town with at least 20 houses.