Dragon Ball: Advanced Adventure

Unbeatable bosses

It is impossible to beat the bosses Mercenary Tao and Demon King Piccolo when first encountering them. Their health bars can be worn down to what would technically be a win but this only triggers an automatic finisher from both which inevitably knocks Goku out. Goku losing to them keeps in line with the corresponding manga and anime chapters as his training to overcome them is an important part of the early story.