OK, this might just be me, but an overpower is something like...
Never-ending Invinciblaty
Never-ending double jumps
One hit kills eggman/you
Stupidly fast speedshoes
Effects of armogedan sheild always on
Never die (God Mode)
Ringpatches (You stand in a sertain area and your rings go up)
Crazyfast thoking
never-ending flight/glide
Thats all I can think of right now!