Xatu + Will + Giratina?
Kind of clunky but if you Xatu someone's active then gust like a Dedenne GX to the active, you can bench Giratina from discard to finish them off, and then get a KO on Dedenne GX for a ton of prizes, assuming Xatu's target was a Tag Team GX.
Great Catcher will be out with these cards so it's not like this is particularly hard to pull off.
EDIT: Would Will apply to Whimsicott GX's ability too? Will doesn't specify that the coin flip must happen immediately after playing the card, nor does it say it must be on your turn. It just says the first time after playing the card, and only for you.
Furthermore, since it says "The first time," that means if I play will on T1 and my opponent doesn't attack a Whimsicott until Turn 4, can I activate Will at that time? It would be the first time a coin flip scenario comes into play since playing the card, so I assume you can just "bank" a Will and hold onto it.