how about this:
Evil being is foretold to come and destroy the world, and the signs point that is going to happen soon.
young hero goes to find some magic thingamajigg to fight the evil monster as it arrives.
grind grind grind... plot plot plot... collect about 8 other characters...
finally they end up in the cave, castle, volcano or wherever the bad guy will come from
now, here is the twist:
through some shady plot devices and implausible writing, the young hero turns out to be the evil being himself (he probably didn't even know that himself), and the characters you hardly cared for the whole game, end up fighting the one you kept powering up all the time, in the final boss fight. 
“It appeared that there had even been demonstrations to thank Big Brother for raising the chocolate ration to twenty grams a week. And only yesterday, he reflected, it had been announced that the ration was to be reduced to twenty grams a week. Was it possible that they could swallow that, after only twenty-four hours? Yes, they swallowed it.”
- George Orwell, ‘1984’
