I submit, basically, any of the Quickenings from Final Fantasy XII. There is basically no limit to what you can do, because every time you use one you have a chance of getting a Mist Charge and thus getting even more attacks, or being able to shuffle and again, get a Mist Charge. You get a ton of those really quickly, and start with a good opening, then you can easily, if you're lucky, rack up a massive chain of nothing but Level Three Quickenings, and do shitloads of damage. And if you can get a Concurrence too, then you can do a world of pain to any enemy. If you master the Quickenings then you can effectively wipe out most of the game's bosses in a very short amount of time, with minimal effort. And the best part is, with six characters in your party, you can do this between four and six times per battle, if you know what you're doing with the Mist Charges, and effectively rain down destruction upon thy foes. And the game is balanced enough that it doesn't normally become a game-breaker, if you're playing normally, but if you put in the effort it can make the game so much easier to handle, it's unreal. One of the best aspects of the FFXII battle system, in my opinion.
