Once per night picks a target. Will take on that person's role in the morning, that person will become the new body switcher. Will fail to switch if target dies at night. Third party.
It's interesting, but need some way that Body Switcher can actually win a game. You said that it's similar to fool, where if it is alive at the end it doesn't win. But fool wins by getting lynched. Body Switcher wins by what?
The Body Switcher can't win, it's a third party. Similar to fool, if it is alive at the end it doesn't win. You win by switching bodies with someone and get their role.