An idea i had some years ago (the original sketches were done in 2005!)
I used 2 references for this, the goku one is from a cover art for a chapter of the dragonball z manga during the freezer saga. Goku wasn't Super sayian in the original though.
The sonic one is from the cover of the archie comics (about the 100th issue i think. again sonic isn't super in that so i changed it as i though the super forms would be more fun then the normal ones.