i have the shiny legendary dog trio (i have multiples actually lol), gamestop celebi, the uh shiny pichu that unlocks the spiky eared one. i just keep them all in HGSS so that i can revisit the events on other playthroughs if i want. they're chillin on my storage copy of heartgold. lowkey kind of want to use those lately to activate their respective events in that game, since i never did them on that particular cartridge.
the only interesting event that i have is the bonus disc jirachi. i got the bonus disc by total mistake, but i still own it and that was actually the first event pokemon i was able to get. i never lived near a TRU growing up, or near any other places where they would host these events back in the old days. the move to wifi has been more inclusive, but i feel like events have lost their appeal. they were at their height in gen 4 and 5 imo since a lot of them activated something in the game and they weren't too high level so you could feasibly use them on an in-game team.