At the beginning of each game the Console must chose a single Boss model. It is the objective of the Heros to defeat the Boss. The boss is summoned at the beginning of the next round after the following conditions are met:
1) all spawning points are destroyed
2) the power gauge fills completely on a 16 bit game
3) the power gauge fills twice on a super game
The boss also introduces a special "Adventure Effects" card to the gameplay. This card describes various changes to the rules, the boss fight effect (when the boss is summoned) and the timeout effect (when the boss has lost half of its health).
In addition, the boss may activate twice in any round that there is at least one spawning point still on the board, and the spawning points stop producing monsters once the boss is summoned.
The boss fight begins by the boss appearing in unoccupied squares at least 10 from any hero. If this is not possible then the boss must be summoned as close to 10 squares away as possible.
In addition to the effects on the Adventure Effects card, timeout causes all status effects on the boss to be removed, the boss is re-summoned in a different location (as above) and a number of monsters are either spawned in its place or moved to its place (if moved they retain their wounds and status effects).
Just like Mini-Bosses, the boss may remove one status effect every time it rolls a heart and inflicts a wound with an attack.