The higher the Intensity, the more monsters there are and the harder the stage is to clear. However, the higher intensity the player sets it to, the better chance the player has of getting more hearts and better weapons. The lowest Intensity on the Fiend's Cauldron is 0.0 and the highest is 9.0. 2.0. is the standard difficulty and does not cost any hearts. Lowering or increasing the difficulty requires the player to spend more hearts. Retreating will make the player lose those hearts.