I like having corpses rise from seemingly no-where, but i think we should expand this theory.
E.g in the darkforest we could have say beings who were imprisioned by a powerful mage becuase they kept cutting down trees.
So when you come close to these trees a spirit would climb out of the tree and attack you. Now these beings have the ability to bypass armour..so its as if you were fighting without any armour at all.
Not to stop there but we could also have a region in the dark forect where they are mountians and the boulders themselves turn into these rock beings. A bit similar to beond divinities earth elementals. Their special trick is to be able to reduce the durability of your weapon by 1/4..
Or maybe Giants/ogres could do that.
It would be fun to see a Giant Heavy orc fight an ogre..
Lets say both of them are wanderers returning home and have an argument.. they start fighting..if they spot you you both turn on you, if not they carry on fighting until they die.