Endgame mechanics

So one of the endgame mechanics from poe 1 that I think would be cool for poe 2 if tweaked a little is metamorph. But instead of making rare monsters to fight for loot it would be cool if we could make our own specter and companions from body parts. Summons would be cool but unsure how to include those. Perhaps with companions the organs would affect the companion auras and with specter maybe the base move sets