You need to get past the fire ruins or you can't successfully finish the game.
There are 3 paths there:
1 Immaculates that you can either convince to let you through or kill
2 Immune to everything demons that you have to sneak past/ run /teleport through
3 Lava + mines (not sure about the last part)
Stuff with a Void Aura won't take any damage - just go past them and destroy the Bloodstone with your Tenebrium weapon.
In the Geomancer's Shop in Sacred Stone is a Book about Tenebrium that gives you an additional point in Tenebrium.
