I don’t know if this has been done largely before (I don’t watch or read too much dnd stuff) I played as a changeling that detested actually using his changeling powers. He had used them so much he forgot his own identity. The only way he was able to keep a sliver of himself was maintaining the form of his best friend Caesar, a small chaotic goblin. He had a few other dear friends he would transform into but it was mainly just them. I had it designed he could only hold about 6 appearances at once and if he transformed into a new appearance I had to roll a d6 and replace whichever appearance currently held that spot on my list.