Rouge the Bat was considered for all three Sonic films. For whatever reason, the writers have just never been able to make her work. Big the Cat almost made a cameo too... as a skeleton in the ...

But there's another character that could show up in Sonic the Hedgehog 4: Rouge the Bat. Rouge makes her first appearance in Sonic Adventure 2, and immediately runs afoul of Knuckles the Echidna ...