Any one like those rare sequences in games where you find yourself having to fight one boss character after another? Or perhaps a boss that keeps changing form/settings?

In War of the Lions, it isn't uncommon to have to play through three battles, although you do have the opportunity to save your progress and modify equipment/abilities. Most of the times all you have to do is defeat the boss character, but the additional enemy units in the battle tend to be very powerful, some times enough to kill your characters in one attack. FFV has dungeons where you can go and get into an Omega marathon if you so wish, fighting one replica after another of one of the toughest monsters in the game.

I also remember the Castlevania Chronicles did actually include a Boss Rush mode to do exactly that, play one boss after the other. Anybody tried that?

Although this is already getting off to another topic, I liked how Shadow of the Colossus had you fighting one massive beast after another.