You said a heir of heart can shape shift? Imagine one who will just turn into peoples s/o so they can get with everyone they want. Not really as terrifying as some of the other stuff here, like exploding your lungs, but i would for sure not like that.

I mean that’s pretty messed up too, you know? That sounds more Selfish though, perhaps a Witch would do that more than a Heir. But yeah, Shapeshift could definitely be a thing Heirs/Witches do with certain Aspects and under certain circumstances. Thinking it that way, isn’t John’s windy poofing technically just shapeshifting into air?