I made it to nationals as a child playing MtG, and in a year of playing local tournaments every week never came less than third (but usually first). The organisers moved town so my scene sorta died out a little and I lost interest, but guess I was decent at that. On a similar tabletop note I've won every 40k tournament I've entered, so not bad there either.
I was in the top 50 Eve Online players for the majority of my playtime and I beat the guy know as the best player (winner of like every single one of their tournaments to date at that point, basically the sonicfox of Eve) live on stage in a 1v1
When I played Pokemon competitively I was generally sat in the top 100 on the ladder, but this one may not be so challenging
There's a bunch of games I THINK I was really good at. But in hindsight I don't actually really know, I mean I could beat my friends buy that probably doesn't mean a lot just that I'd played more than them. Games like Tony Hawks Pro Skater, Need for Speed Underground 2, Halo 1, etc
I'm above 4k MMR on Dota which isn't huge but is decent and puts me in the top 1%-5% globally I believe.
Calibrated Platinum on Starcraft and got close to Diamond I believe. Still something I've gotta pick back up.
I THINK I'm good at Dark Souls, but I'm not really sure. My friend who plays literally nothing but the Souls games gets me to beat bosses he can't clear (like Smough and Ornstein on NG+ ) and I've beaten all their games starting with Demon Souls now, and beat DS2 without ever using a shield which people told me would be crazy hard
There's a bunch of games out there in decent at but don't play enough to really call myself dope at. And I guess you could say I'm good at MKX.