Sonic and Sally's interaction in the last half of the last episode. Up until then, Sonic insisted on taking on Doomsday alone. Especially since the only chance left to stop Doomsday was to use the Deep Power Stones to unleash a massive explosion. Since Sonic had already used his supply of power rings, this was basically a suicide mission. Then Sally tells him that they're in this together, however it ends, showing that she's willing to die with him. Sonic accepts her help. He even kisses her hand!
Right at the end, there's this bit:
Sonic: No more Robuttnik. Too bad.
Sally: What? "Too bad"?
Sonic: Hey, without a villain, what are heroes gonna do?