Ben 10 Ultimate Alien: Cosmic Destruction Hints for PlayStation 2
This doesn't take much energy. Use Way Big's long range special attack, and just hold it. The enemy can't break away and you can just hold that blast forever. After the cut scene and mini game, repeat the whole process until you win.
When he tries to hit you just side step to dodge his attacks and when you deal enough damage there will be a quick cut scene you will be back at the lake, do the same thing until he dies.