X2, also known as X2: no Relief or Project X2, is a 1996 shoot'em up for the PlayStation by Team17 and Ocean Software (and by Capcom in Japan).
It's the exclusive sequel to the 1992 Amiga hit Project-X. Allegedly, Capcom collaborated also in the re-design for Japanese audiences.
The final boss of Taekwon-Do for the SNES will break the rules of the game and destroy the ref from the jump. I wrote an FAQ for this game back in the day.
Asura Buster: Eternal Warriors features a hidden "Ghost" system where, if you finish a round with a Super Move while your health is below 10%, your character remains in a semi-transparent state for the next round, gaining a slight speed boost.