This is a weird one, but:
In Nightcrawler 11 (and one two-page spread in 12), there's an interesting conceit. It shows an increasing number of floating heads around the page borders of alien kids floating around the page borders.
Thing is, most (if not all) those kids are analogues of Marvel heroes - Beast, Iron Man, Armadillo (!), Mystique, Sunfire (female), Jocasta, etc...
I swear one of them is a Guardian.

So, not quite an appearance, and not quite certain, but it's there.

~ Le Messor
"A thick skin is a gift from God."
~ Conrad Adenauer