Super Saiyan 3 has been used by Gotenks, but the form was unstable and short-lived. Neither Fusion Dance nor Potara Fusion can sustain Super Saiyan 3 for long due to the immense power output.
Since it is canon, though, a new development has just shaken the Dragon Ball fanbase to its core: in this week's episode, Goku transforms into his Super Saiyan 4, making the transformation part ...