Frog-O

Frog-O is the shady hybrid stuffed animatronic commissioned by yellow guy. He wasn't officially released into a game until Feef 7, but some skeptics think he could be the mysterious green guy lurking around since Feef 2. (known for his off white tinted green text)
But this is all just speculation. There has also been a brief appearance of a golden Frog-O if you collected all the frog leaflets through Feef 7. The Feef fanbase still don't know the meaning of his appearance, but are still trying to deduce it.

(Golden Frog-O)