Ultra SSJ

Not to be confused with Super Saiyan 2, this is the level "which surpasses the level of Super Saiyan." When Goku trained in the room of time during the Cell saga, he discovered that he can increase his power almost 3 times more than normal. But he realized that while this increase makes him more powerful, it also makes him slower. This is the major weakness which means that it is no good in battle.
Who can transform at this level: Goku, Trunks, Vegeta