If you are low on health, save your game, then shut off the power and turn it back on again. When you appear back where you left off, you'll be back at full health/Ki.
Infinite Health
When an enemy attacks you with an energy attack, press the R button to fly. When you are hit, Goku will land but your flight meter will still show. This allows you to have infinite Health. You can deactivate the glitch by pressing the R button to fly and hitting it again to land. Though you cannot see it, your Ki will go down when you shoot it.
