Majuub

They didn't even mastered SSJ2 in order to go SSJ3 that's why they have an enormous Ki drain, Goku just pushed the limits of his body. That's why I said mastering a SSJ3 is somewhat possible since they'll never be able to reach it due to the massive drain the SSJ3 impose, if you still have that Ki drain while in SSJ3, then don't even think going SSJ4 will be possible. The first step would be to at least get rid of that drain and to control the SSJ3, Goku can't even do that. That's why I say MSSJ3 would be possible, it's not like they couldn't handle theirselves as SSJ2. Gotenks didn't seem to have the same probleme as Goku did since he was really powerful, he didn't deal with the Ki drain. I think it's safe to assume that if Goku could handle it like Gotenks did, he would be in the same league as SSJ3 Gotenks. Now multiply the power of SSJ3 Gotenks by 5x and he is beyond Shin Buu and even Shin Buu(Gohan absorbed). I believe Goku would still be fairly weaker than SSJ3 Gotenks, but he would be much stronger than SSJ3 Gotenks, Shin Buu or Gohan.

SSJ4 Gotenks>>>>>SSJ4 Goku>>Chou Gohan>>>SSJ3 Gotenks>Shin Buu>MSSJ3 Full Power Goku>SSJ2 Gotenks>>MSSJ Gotenks>SSJ3 Goku>SSJ Gotenks

I really believe that, if Goku could perfectly handle the SSJ3 than his power would have to be really really great.

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