In the Empire Strikes Back, Darth Vader took Luke Skywalker's hand. What happened to the hand? Well, in legends, the Empire had it, along with the lightsaber. The hand was taken to Emperor Palpatine where he had it cloned and created Luke Skywalker's evil dark side twin.
what If Palpatine does this in Episode 9? Then transferring his essence into the young Luke Skywalker, he fights Rey and Kylo??