Before I dip, I'm gonna share another nasty set-up that's sealed me matches in tournament:
During low percents, down-throw your opponents a few times on stage. Make a mental note of their reactions. If they don't tech or get-up attack, that's exactly what you wanna see. In order to prevent them from being conditioned into actually doing a get-up attack, make sure you don't try to chase them at low percents after down throw if you want this kill set up to work. Here's the fun part: by this point, hopefully you're in the prime position of having an opponent who doesn't tech or attack after down throw. Since Sonic's down-throw puts the opponent straight forward on the ground, you can get a running up-smash on them if you time it right, which kills a lot of the cast at a pretty decent percent, even more with rage.
Sorry for such a long-winded paragraph. Basically, if your opponent doesn't react offensively after down throw, you can get an up-smash tech chase.