With the notable exception of the very first Boss Challenge in the game, which had mostly different mechanics and which ended once the last battle tile was won, all subsequent Boss Challenges have different Elemental restrictions while the battles are based on regenerable laps, with each lap consisting of 4 main battles and 11 regular battles.
During a Boss Challenge, players can earn a main reward by defeating Boss-like Dragons and smaller rewards by defeating regular Dragons. The main rewards can be in the same amount for all Boss-like Dragons, or they can increase with each Dragon defeated, while the amounts given for defeating regular Dragons are based on the Level Modifier. The Elements that can be brought to the Boss Battles are restricted, starting with all Elements allowed for the first battles. Defeating a Boss-like Dragon reduces the allowed Elements by taking away 1 random Element, making the restrictions more severe after each Dragon. The Divine Element is the only non-random Element, being allowed in all battles. The hardest battles allow only 3 Elements: the aforementioned Divine and 2 other random Elements, that change each time a Boss Battle is won. The Elemental restrictions can be refreshed , but there is a waiting period of 2 hours before the next fight can start and it will only last until the next Boss is defeated. Every battle requires a cooldown period of 2 hours to pass before the next battle can be joined.
When a lap is cleared, a reward is given and the map resets with a new set of battles. Once the 4th lap is completed, the player is rewarded with a Dragon. Any subsequent lap after the fourth one offers a repeatable reward. Boss Challenge laps are unlimited with infinite rounds.
Any waiting period can be skipped through the use of Gems, starting at 9 Gems and then gradually decreasing. The enemy Dragons are entirely random, thus not all players face the same Dragons. In most cases, the only Dragons encountered by all players, in the same battles, are the main opponents. The levels of all opposing Dragons are in relation to the levels of the player's own Dragons at the moment a Boss Challenge started.