Ive been trying some different combos.
I tested down throw > Bair spike > instant Uair
I just found this thread, so I guess Indigo found this similar combo earlier.
This only star-ko's (sorry is that the term when a flash emits from the enemy before they are ko'd) at 9-10% earlier than down throw > Uair, but is really satisfying if they miss their tech.
At lower percents like 30-50, If youre opponents doesnt air dodge while DI'ing away, you can A. down throw > sour Bair > spike Bair if they are offstage, or B. Onstage Dthrow > sour Bair > sour Bair, which might be able to be followed by a reverse psi magnet, but I havent tried. Otherwise you could just use option A onstage too, if they miss tech, you can follow up with Dair, fast fall Nair or another Bair.