Stages

Fiend's
Cauldron

The Fiend's Cauldron appears at the start of every stage. By pouring hearts into the cauldron, you can increase the intensity of the stage. More intense stages contain stronger enemies and are more difficult to clear, but you are also more likely to acquire rare and valuable weapons while playing them.

If a stage gets too difficult, Pit will declare "I'm finished!". The hearts you staked will be spilt from the cauldron, and the intensity of the stage will decrease. This means that the value of the weapons you pick up will be lower, but it also means that the stage will be easier to clear. If you want to get your hands on the very best weapons, however, you'll have to pour a lot of hearts into the cauldron and clear stages without spilling any.

Decreasing the intensity of a stage to below its default level (2.0) means that you will hardly face any enemy attacks. Note, however, that this will actually cost you hearts.