The Boss Pit allows you to battle one Boss at a time. Each Boss has three stages, which get progressively more difficult. You can only play one stage per day. You can have five attempts in each stage. If you are unable to defeat the Boss in those attempts, the Boss will reset and you can choose a different or same Boss on the following next day. Each boss spawns enemies and "throws" them at you. Enemy you defeat will decrease the Boss' health. However, each enemy can only be damaged by a specific type of damage. Focus on using fighters that cause damage. You can also consider the Healer to keep your party healthy and or the Crimson Witch for her bonus and increase in attack speed. Bring your highest level heroes to a Boss battle, even if you do not have the optimal damage types. The Boss will be damaged after each enemy killed. You do not have to kill all of them in order to win. Start on the highest difficulty setting and gradually drop down until you can defeat a particular stage. Although rewards are better at the higher difficulties, getting some sort of prize is better than nothing.