It would fit well into any deck that generates tokens or simply prioritizes having a lot of creatures in play
Legacy and Vintage are great formats, and most players would be perfectly fine with playing against opponents with some number of proxies in their decks if it meant they could play their favorite format on a regular basis
The Darkrai SIR is the safe, obvious chase, but Zeraora is the one with a data point suggesting it can hold or gain while the set cools
Unlike similar cards in the Scarlet & Violet era that contained comparatively muted colors and designs, Mega Evolution kicks off these cards with bold colors that uniquely express the Pokemon
It also digs in a 100-card deck and puts stuff into the graveyard for recursion, so it's synergistic with the format and various archetypes like Golgari Reanimation
On top of that, hexproof from mono-colored makes it resilient against most removal