2 reasons,1: you cant do it in world tornaments because that would be cheating(two against one)2:you cant do it if your oppenent is gaurding

you have to have fusion (gotenks) on goten or kid trunks
then select custom then in battle have 3 or more ki gauges
then press square square triangle triangle circle and
press the buttons in order to have cool gotenks!
if you get it wroung you will be fat gotenks with
no moves!

He's right

I agre whith the first 2 guys.ROCK ON