How does Star Crossed work when it gets rebuttal by a Mel deck?

It depends on what you do when Rebuttal resolves — and you decide then, not when you play it.

Rebuttal (Mel's signature, [1] Mind/Chaos) can target Star-Crossed since its Energy cost of 3 is within the "no more than [4]" limit. On resolution, you either pay [A] to take control and make new choices, or decline and counter it (FAQ 12038).

If you take control, "friendly" and "enemy" re-anchor to you. Star-Crossed's two targets are both mandatory — you must pick one unit you control and one your opponent controls — so you can retarget either or both slots, but you can never bounce two of your opponent's units. If you decline the [A], Star-Crossed is simply countered and does nothing (Rule 425.1).

One catch: Star-Crossed must still be on the chain when Rebuttal resolves — if it was already countered or removed, Rebuttal fizzles and you keep your runes (FAQ 12069).