Bloody Palace is a battle arena mode similar to the same bonus mdoe from DMC3 SE. The player battles through 101 stages, the player can choose to play it as Nero Super Nero, Dante or Super Dante in Normal or automatic mode.
When you enter enemies appear, defeat them to open a portal to the next arena. New to the palace is a time which counts down during the fight if it reaches zero it's game over. Defeating enemies gives you a small time bonus. Bonuses are also awared for clearing a stage while suffering no damage and by killing enemies with a stlyish rank.
Every 10 stages there is a boss, at stages 10, 30, 50, 70, 90 the enemies are grouped difficulty enough to be considered bosses. Stage 99 is also done in this manner. in stages 20, 40, 60, 80 and 100 you fight story bosses like Berial.
Stage 101 is Dante in quote "His most powerful and dangerous form" So I'm assuming Dted dante at 101. If you're playing as Dante you fight an evil shadow Dante (kinda like the Red Vergil I'm assuming).