The Master Core is the final boss in the video game Super Smash Bros. for the Nintendo 3DS and Wii U. It is the true form of Master Hand, and the player can only encounter this boss on Classic Mode on Intensity 5.0 or higher.
When the player is playing Classic Mode and managed to reach the Final Destination, on a certain difficulty, they can choose to confront both Master Hand and Crazy Hand at the same time. On at least 5.1 difficulty, after the two Hands are dealt 70 HP worth of damage, Master Hand tears open to reveal the shadowy core inside covered by the Swarm called Master Core with Crazy Hand disappearing. The Master Core is a formless entity that attacks the opponent in various ways. It can take on many forms. If the player manages to deal enough damage to the Master Core, the Core will revert back to it's true form; Master Core. When it's in it's Core form, the player has to destroy it before it unleashed a one-hit KO move. Once the player deals enough damage, the Master Core is defeated.
Each form of the Master Core has various abilities.
The Master Giant is the Master Core's most powerful form. This form can only be seen on Intensity 7.5 or higher. The Core takes the form of a large humanoid creature. It attacks by firing energy balls from its forehead and grabbing players with its hands or its forehead. the Master Core is also capable of moving the stage vertically to try and get the player hit by its other attacks.
Master Core attacks the player by firing spikes out of the ground, chomp at the player from the background with its large jaws, and do a full-body stomp that causes the stage to tilt for a few seconds. It also generates electrical discharges as well. This form can be encountered on Intensity 6.0 to 7.4, or when Master Giant is defeated.
Master Core takes the form of multiple swords. The Swords can attack with either homing attacks, or perform slashing attacks. They can even generate energy slashes. This form can be encountered on Intensity 5.1 to 5.9, or when Master Beast is defeated.
Master Core takes the form of a shadowy form of it's opponent. It is slightly bigger than its opponent, and it's attack's are slightly stronger. However, as the Core takes damage, it gets smaller and smaller. This, form appears after Master Edges is defeated.
The Master Fortress is a form that's available only in the Wii U version of the game. In this form, Master Core takes the appearance of a huge fortress with enemies and orbs to hit to make new paths. When the Fortress appears, the player receives a heart to replenish their health, and timer is reset. In order to defeat this form, the player(s) must destroy all the cores within five minutes. It's very similar towards the Smash Run on the 3DS version. The form is its most powerful incarnation in the game and appears on intensity 8.1 - 9.0 after the Master Shadow.
The Master Core is at its weakest. It becomes vulnerable and stationary at the center of the Final Destination. It can't attack its opponent. When the player attacks the Core, it won't retaliate. Continue to attack the Core, and it will eventually be destroyed. However, if the player doesn't destroy the Core within a certain amount of time, it will unleash a one-hit KO attack, similar towards Tabuu's Off-Wave attack. If the player has an extra life, the Core will continue the move about five more times until it self-destructs. Fortunately, much like Tabuu's Off-Wave, if the player performs either rolling dodge, or the sidestep dodge at the right time, then the player can survive the attacks. This form appears after either Master Shadow or Master Fortress is defeated.
During the battle the background music will occasionally go silent and a few quick beeps will play. Those beeps are actually Morse code and spells out "Master Core".