Boss Battle Trick

From Glitches

From the game Dark Savior for the Sega Saturn.

If you keep using the sword on a boss over and over again by mashing the button and pressing into him/her, you can sometimes end up "inside" of the boss where you can keep attacking it, but it can't attack you. This is especially easy to do on M-Bilan, because he's so big.

Taken with permission from Flying Omelette.