Dawn of Sorrow (2005), the first installment of Castlevania on Nintendo DS, is a direct sequel to GBA hit Aria of Sorrow. Everyone is trying to kill our hero Soma Cruz, since in the previous game he absorbed all of Dracula's attributes. You can always trust weird cults to try and bring about the end of the world by unleashing this power.
The game is so fully broken at this point though, that there really is no plot in this run. Or final boss. Or much of anything at all. Using improved versions of the glitches used in its predecessor, this movie completes the game in half the time. More details about the glitches can be found in the author's comments.