Boss Battles Mode is an Unlockable Stadium mode introduced in Super Smash Bros. Brawl, which is very similar to All-Star Mode, except that, rather than fighting all the characters, all the bosses are fought. Boss Battles Mode is unlocked after the player completes both Classic Mode and 'The Subspace Emissary' for the first time, or in other words, has faced each boss other than Crazy Hand at least once. The goal of Boss Battles Mode is to defeat every boss in the game with a single stock, or two characters in its Co-op mode.
When a player begins Boss Battles Mode, they are immediately dropped into combat against a boss. Once the boss is defeated, the player is brought to the rest area. The rest area displays all defeated bosses as trophies, a screen that displays the face of next boss to be fought, and has three Heart Containers (five in Co-op mode), which, like in All-Star, do not reappear even upon later visits to the rest area. This format continues until all bosses are defeated.
However, the player is not allowed to continue after using their stock up, as it is a Stadium Mode. The battles occur in random order, except for the battle with Tabuu, which always occurs last. Each boss has their own Stamina Bar as one would normally fight them in the Subspace Emissary, including both of the Hands. The final three bosses before Tabuu move and attack at a faster rate (most noticeable with Rayquaza and Galleom). The player is treated with a picture of one of the bosses upon completing Boss Battles: this picture varies depending on the difficulty level chosen. Stickers cannot be in Boss Battles.
The battles in this mode include:
- Clearing Boss Battles with 10 characters gives the Subspace Gunship trophy.
- Clearing Boss Battles with 20 characters gives the Jyk trophy.
- Clearing Boss Battles with every character gives the Winged Tabuu trophy.
- Clearing Boss Battles on Easy difficulty gives the Subspace Bomb trophy.
- Clearing Boss Battles on Medium difficulty gives the Shadow Bugs trophy.
- Clearing Boss Battles on Hard difficulty gives the Dark Cannon trophy.
- Clearing Boss Battles on Very Hard difficulty gives the Porky Statue trophy.
- Clearing Boss Battles on Intense difficulty gives the Galleom Tank trophy.
Differences between the Easier and Harder Difficulties
- Bosses have more health.
- The bosses move at a faster rate.
- The bosses are more powerful.
Boss changes from other modes
Several of the bosses are slightly altered from their appearances in other modes:
- Crazy Hand is a boss by himself, rather than together with Master Hand.
- Master Hand and Crazy Hand have Stamina Bars like other bosses, rather than the usual HP shown at the bottom.
- Galleom will be fought randomly in one of his two stages. Its death animation will depend on when the player fights him. If they fight him as one of the earlier bosses, he will kneel to the ground, defeated. If he is fought as one of the last bosses before Tabuu, he will fall backwards to the ground.
- There is no time limit when fighting Meta Ridley, or any of the bosses.
- On Easy, Normal and Hard modes, Tabuu's Off Waves do not OHKO the player.
- In lower difficulties, all the bosses' speed, attack power and health are greatly decreased.
- Petey Piranha's cages are empty, as when he is faced in The Great Maze stage of The Subspace Emissary.
- The sky is clear when fighting Petey in Boss Battles, rather than covered in dark clouds.
- The individual boss themes are replaced with generic music, Boss Battle, except for Master Hand, Crazy Hand and Tabuu. They use the music Final Destination (Melee), Giga Bowser (Melee), and Boss Battle Song 2, respectively.
- Items do not appear.
- The camera behaves as it does in normal Brawls rather than as it behaves in the SSE.
- After a boss is defeated, players will not lose a Stock going past the blast lines.
- Despite having a boss trophy appear in the background of the resting area after each victory, players do not "earn" those trophies.
- The Boss System works like the one in the game Kirby Super Star and its remake, Kirby Super Star Ultra's, sub-game, The Arena, where Kirby had to fight bosses in a random order, except the last one, the hardest one.
- The player can move and attack before the Announcer shouts "GO!"