Every boss drops a trophy, and hanging it at the sacrificial stones unlocks a Forsaken Power. You can only have one active at a time, and swapping is free, so the real skill is knowing which to run when.
The powers
- Eikthyr. Big reduction to stamina use when running and jumping. The travel power, and superb early.
- The Elder. Faster tree chopping. Sounds dull, is excellent when you are gathering a lot of wood.
- Bonemass. Large physical damage resistance. The melee fight power, and arguably the best in the game.
- Moder. Constant favourable wind for sailing. Transforms long voyages.
- Yagluth. Elemental resistance, for fire, frost and lightning.
- The Queen. Reduced Eitr regeneration cost, for magic builds.

What to have active, when
- Exploring on foot: Eikthyr, every time.
- Sailing anywhere: Moder. It is the difference between a long trip and a very long one.
- Any melee boss: Bonemass.
- Chopping for a build: The Elder.
- Ashlands and elemental fights: Yagluth.
Swap before you leave, not after
You can only change powers at the sacrificial stones, which are usually nowhere near where you need them. Decide what the trip needs before you set out.
For the order you unlock these in, see the progression guide.