SMM2 Rolling Snowballs | Ninji Speedruns | 19.994 seconds
it took me like an hour and a half of non-stop practice to do. I was stuck at 20.005 for over half of that time, but oh MAN was I excited once I finally achieved under 20 seconds and get gold.
I'd recommend doing this run if you're good at Mario Games. Maybe just go for silver at 22 seconds though. It's a LOT easier