It could be an interesting tool for a flash deck utilizing threats like Brineborn Cutthroat and Nightpack Ambusher or could work with various instants that make tokens like March of the Multitudes, Raise the Alarm, and Secure the Wastes
It has some powerful abilities that could show good results in commander, but eventually it has been deemed as a deceptively good card
You can use Aerodactyl VSTAR's Ancient Star attack and then switch out another Pokemon to the active spot, since Aerodactyl VSTAR keeps the ability active even if it's not your active Pokemon
Of the two, Lost Box strikes me as the most versatile, but Gardevoir does tend to have the advantage in the direct matchup, thanks to Manaphy and Jirachi
Waiting to gain life from Wall of Reverence, another end of turn trigger, wont work because we have to choose the target when we put Celestines ability on the stack