He doesn't Trunks and Goten can only transform when they are fused because the fusion technique gives them more power than they have alone. You may have seen fan art with Trunks and Goten as SSJ3 but it never happened in the anime.
Episode 230 "Super Saiyan 3"
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Never
Never. :(
Goku does not turn super saiyan 6 or 5 in fact. and it only goes up to super saiyan 3 in the manga and super saiyan 4 in the cartoon.
230. Super Saiyan 3?! no it's episode 245 because i just watched it
No. His super saiyan 3 form is only in DBZ Raging Blast 1 and 2. Sorry!
Episode 245 "Feeding Frenzy" Somewhere around the end Gotenks turns into a super saiyan 3
Perhaps. As said in Dragonball Gt, in order to turn to a super saiyan 4, the saiyan needed the proper physical condition (Power level Most likely around super saiyan 3 level) then receives causing the transformation to a golden great ape which the saiyan must find himself in the beast to transform to a super saiyan 4. And since gohan is stronger than a super saiyan 3 in mystic (Ultimate gohan) mode, he may turn into a super saiyan 4 However due to the fact he is a half saiyan he may not transform (Although this is not confirmed) Once again, however he did turn into a great ape in the saiyan saga in Dragon ball z so with his major power as ultimate gohan, he should turn into a golden great ape and then to a super saiyan 4.
Only in the video games
there is not a super saiyan 2 gotenks. He can only transform into a super saiyan and a super saiyan 3.
Majin Goku