The battle will be made up of a timed stage where the player can attack Monstro directly, and an acid-filled stage within Monstro's belly where the player is sent once the three minutes run out. The player must defeat the Unversed within Monstro to escape and try to damage Monstro further.
- Monstro swallows the character into his belly, and force the character to battle Unversed in order to get out. The battle will start at his belly, but if it does happen again, the area will be filled with acid, that can damage the character.
- Monstro jumps out of the water to swallows the character, and then shoots the character out of his blowhole.
- Monstro slams the water to create damaging tidal waves.
- Monstro body slams the island that the character is on to cause damage.
- Monstro swings his powerful tail down on the character.
- Monstro charges at the character's direction to knock the character off the island.
- Monstro attempts to inhale the character in and spits the character out, if successful.
Monstro is a unique Mirage Arena boss. The battle begins in a stage within Monstro's belly where the player must defeat the Unversed within Monstro to escape. Once all the Unversed are defeated, the true battle begins as Monstro spits the player out.
Monstro is a tough opponent in battle as he has high HP, and compounding the difficulty is the fact that the player is only given three minutes to damage him as much as possible and the arena consists of small islands. In terms of offense, Monstro will slam the water to create large, damaging tidal waves. the boss will also body slam the island the player is on to cause large damage, as well as slam his tail down on the player.
Monstro will charge directly at the player to knock him or her off the island. And lastly, the boss will attempt to inhale players in, and if successful, spit them out via the blowhole, causing damage. The player can stop this attack by throwing an explosive barrel at him, knocking him out. At this time, the player can cause the most damage to Monstro.
To damage Monstro, the player can throw the explosive barrels at him when it rises above water, and should use distance attacks such as Shotlocks, and fire commands. The best way to damage him is to use Mine Square and/or Mine Shield. When his body slams or slams his tail to you, dodge it and then use Mine Square. After three minutes of combat, Monstro will swallow the player, where he or she must defeat the Unversed to escape and damage him further. However, the arena is now filled with acid, which can damage players. By repeating the above strategy, Monstro will fall with relative ease.
|style="-moz-border-radius:10px"|Monstro (Kingdom Hearts Birth by Sleep Final Mix: Monster of the Deep) |- |style="-moz-border-radius:10px"| |}
|Bosses introduced in Kingdom Hearts|
|Queen of Hearts, Card Soldiers, and Crank Tower | Cerberus | Hercules | Hades | Rock Titan | Ice Titan | Sabor | Clayton | Cave of Wonders Guardian | Jafar and Genie | Genie Jafar and Iago | Lock, Shock, and Barrel | Oogie Boogie | Oogie's Manor | Glut | Ursula, Flotsam and Jetsam | Captain Hook | Maleficent | Dragon Maleficent | Chernabog|
|Bosses introduced in Kingdom Hearts II|
|Shan-Yu and Hayabusa | Beast | Hydra | Pete | Captain Barbossa | Shenzi, Banzai, and Ed | Scar | Scar's Ghost | MCP and Sark|
|Bosses introduced in Kingdom Hearts Birth by Sleep|
|Lucifer | Magic Mirror/Gameplay | Experiment 221 | Gantu | Peter Pan|
|Bosses introduced in Kingdom Hearts Birth by Sleep Final Mix|