You know writing is my ****. i'd love this.
We can't play the symbol option though, did that already Captain Marvel.
So we'd have to go deeper. A cameo. Somebody recognizable. And somewhat flashy, but not cheesy. Someone like nightcrawler.....Or Mystique showing a Krull how she changes into people too..
or if they really wanna make people lose their ****..
a blurry pic or a darkened room...and the voice of Ian McKellan saying 'Ohhh...Charles...they've been busy' ..and you see a distorted vision of a guy and another in a wheelchair