Alright, idea #593: A modern-day RPG about psychics. I didn't have much of a plot (there's an Eleven-esque girl who runs away from an evil organizations and gives the protag, and allies he chooses, psychic powers, which they use to fight the organization and get help), but I did have a main mechanic.
The Will meter, which is basically the MP meter, is both an escalation mechanic and a corruption meter. It starts at 0% at the start of the fight, but as you use abilities, it goes up. As it increases, the character it's attached to get bonuses to attack, defense, speed, etc. They also get bonuses to their skills, increasing their power and adding modifiers to them. Once you hit 100%, you can even use special limit-break-esque attacks. However, there's a maximum cap of 200%. Once you get higher than 150%, your character goes berserk, and starts using attacks indiscriminately, and their boosts are obscene. Once they hit 200%, they're stunned for a while, and then they wake up at 0%.