I've actually managed to get 100 once. It took me a whole lot of tries, though. I did it on one of the Lizards in Star Hill, and it took something like 2500 dammage! O_o

Anyways... you get the Super Suit. The absolutely perfect armor. Too bad, the game was really easy even without the Super Suit, so I didn't need it at all. It's still cool to have it, though, on my "mastered" save file.