I was playing my AMU with absolutely no mewtwo-counters of any sort. My opponent on the other hand played AMU with mewtwo lvX. So I was pretty sure I was going to lose this, I didn't have Palkia lvX at the time, so if the Mewtwo were to be active, I would have been done for. Otherwise it would've just been a mirror match, so 50-50.
1st round, he gets a lone mesprit, I get Uxie, 40, he does nothing his turn, 40 again, win.
2nd round, he gets out Mewtwo, I'm doomed.
3th round, he starts with another mesprit, I get Azelf, 40, he does nothing again, 40 again, win.
I went on to winning that BR whilst I totally shouldn't have won that match ._.
Probably one of my weirder victories, and the only one I remember...