Gotenks Super Saiyan 4
Gotenks is the fusion of Son Goten and Kid Trunks.
Gotenks Super Saiyan 4 (Orange hairs version)
Gotenks could hypothetically reach the SSJ4 level only if kid Trunks and/or Son Goten would have grown their tail back.
Below is a fight in Dragonball Z Budokai Tenkaichi 3 between Gotenks SSJ4 with classic reddish hairs and an enrolled tail and Vegeto SSJ4.
Gotenks SSJ4 (Black and white hairs version)
Here is an other look for Gotenks SSJ4 (depending whom between Son Goten or Trunks have had his tail back). In his SSJ4 form, Gotenks tail is always orange like his fur (in the picture below, Gotenks SSJ4 tail can be seen enrolled around his body).
Others pictures from Gotenks Super Saiyan 4
Gotenks SSJ4 ingame pictures from the game Dragon Ball Z Budokai Tenkaichi 3 (Mod) :
Kid Trunks and Songoten with a saiyan tail perform the Fusion dance in Super Saiyans to become Gotenks :