There is a little luck involved, but it's mostly down to timing. You have to understand the tools available to you and use them appropriately. You should have a Dazzle Blast, which will help somewhat (though it isn't necessary strictly speaking). The main thing though is to pay attention. Do the multi-hit attack, keep track of where it's landing. If an enemy is likely close to death, it may be worth it to use an ordinary attack to immediately down him rather than waiting for a recharge. Then just use your full heals (hamburger) strategically at the right time. GT fights are about speed: you're racing the enemies to a win condition (Them all being dead). You're trying to survive while winnowing them down quickly. If you waste health items at the wrong time, or attack in a way that's not efficient, you'll probably lose.