Suggested by Anonymous Mothra is another foe who will end up defeated by the heroics of Sonic. Sonic is way too fast and clever for Mohra to hope for a victory. Mothra is no slouch in the speed department either but the gap is too wide. As such, it will be game over for Mothra as soon as the match begins. If Sonic wants to end the round even sooner, all he has to do is activate his Super Sonic form. There’s really nothing Mothra can do against it. Sonic wins.
DReager1.com 
Ok, now what about default versions?
I’d still go with Sonic although it’d be a little closer. His attacks wouldn’t deal a whole lot of damage but they’d get the job done
Mothra vence porque ela é mais inteligente,resistente,ela pode refletir os poderes de sonic,paralizar,atordoar poderes são muito poderosos.sonic pode ser rapido mais não é mais inteligente que ela.você ta subestimando a mothra.ela E muito mais forte do que você pensa e ela E monstro heroico e não vilão.e é muito injusto o sonic usar super por que a mothra não tem transformação.
It may not be super fair but at the end of the day Sonic just has a lot more combat forms and abilities at his disposal here. It’ll be difficult for him to be brought down