It's not that well known, but the Limit Breaks from Final Fantasy VII were based on a hidden mechanic from the previous game. When a character's health was less than 1/8 maximum, there was a 1 in 16 chance that choosing to attack as normal would instead unleash a hidden ability unique to each.

See, for example, Relm's Star Prism. The young girl unleashes multiple star-shaped projectiles that swirl around an enemy and detach its soul from its body, whisking it away to places unknown while the vacant husk is left to rot.

Credit where credit is due: the background is from the game itself (Esper Cave, where Relm first joins the party after dealing Ultros a humiliating defeat); character and game are (c) Squaresoft/Square-Enix.

Incidentally, trying to get even close to recreating any character design by Yoshitaka Amano is an exercise in hair-rending frustration. Anyone who complains about Tetsuya Nomura "destroying" Final Fantasy character designs with all those belts and zippers needs to take a look at Amano's relentless use of beads, sashes, and barely-avoided female nudity.