Mine was only a few months ago in Ultimate.
One day I was trying to learn Sonic in Quickplay (I’m sorry) and lost a TON of GSP—literally millions. I stopped for the day.
The next day, I return to Quickplay and decide to queue for team battles to see how I would do with a teammate. I get a team battle and my teammate is a Cloud who turned out to be almost exactly at my GSP.
We STOMPED. This was back when you would keep the same teammate if you both rematch, and we kept going. We won I think 10 games in a row (minus a FFA somewhere in the middle) and climbed millions, almost all the way to elite. I sent him a friend request after we were done, which I rarely do.
Every time I see a Cloud online, I remember that day. It was the most I’ve ever improved with a character in one day and the most fun Smash session I’ve ever had.