!ask do you have to move a unit with shuriken flip

Yes — the move is mandatory. Shuriken Flip's "move a friendly unit" is a required target (Rule 355.10), so you can't play it without a friendly unit in play, and when it resolves you must move one. Only the "Deal 2" half is optional ("up to one" allows zero targets), so you can fire it off just to reposition a unit even with no enemy on the board (FAQ #11682). If the friendly unit becomes an illegal target (e.g., leaves play in response), the move instruction simply fails to execute rather than fizzling the whole spell.