The Eikthyr and Bonemass powers can be literal lifesavers, and are extremely useful in general.

I'm currently in the bronze age, exploring any Swamp I find. The Eikthyr power is amazing against abominations, because I prefer to fight them with fire arrows (especially now that I have acquired full root armour) and that requires me to stay at a distance.

The Bonemass power is amazing for fighting stone golems.