What do you think of the idea that metaphorically or literally: Witches/Heirs become one with their aspect at a *physical* level and Mages/Seers become one with their aspect at a *mental* level?

You could make an argument for that but then again it’s a case by case basis. Heirs/Witches may ‘become’ one with their Aspect as it fits under the definition of Changed- Being Changed by their Aspect and Changing into their Aspect or as an Embodiment of it, it’s a thing that COULD happen, but it’s not a NECESSITY I feel. The Mage/Seer one is even more muddy, because becoming one with the Aspect at a ‘Mental Level’ is incredibly more abstract, not to say Homestuck argues that reality reflects your Mind and Will so technically the separation between Mind and Body is even more dubious. All in all, it’s easier to say that Seers and Mages get to know their Aspect intimately, but not necessarily that they… Become one mentally. Aspects are a part of reality after all, they may embody ideas, but they’re abstract concepts, and you can’t quite ‘mentally become’ something so expansive and abstract.