Master Core

Master Core is the final boss of the Classic Mode in Super Smash Bros. for Nintendo 3DS and Super Smash Bros. for Wii U.

In Super Smash Bros. for Nintendo 3DS, Master Core can only be fought on intensity levels 5.1 and higher, but only if the player takes the black route to face Master Hand and Crazy Hand together; Master Core will not appear if the player is only fighting against Master Hand. When playing on intensity 8.0 or higher, however, the player can only take the black route, making the Master Core battle inevitable.

In Super Smash Bros. for Wii U, the player does not have the option to avoid fighting Master Hand and Crazy Hand together, and as such, on intensities 5.1 and higher, Master Core must be fought.

During the final battle between the player and both Master Hand and Crazy Hand, once Master Hand loses a portion of his stamina, Crazy Hand leaves, and Master Hand's glove rips open and reveals Master Core.

Master Core is hidden under a mass of black particles called Swarm, that take on a variety of different transformations and forms during the battle, each form doing a different attack. The forms that Master Core uses include a humanoid known as Master Giant, a monster known as Master Beast, a group of swords known as Master Edges (Master Sabres in the British English version), a clone of the fighter known as Master Shadow, and the true Master Core itself.

The initial form of Master Core depends on the intensity level. By setting the intensity to 7.5 or higher (7.0 or higher in Super Smash Bros. for Wii U), Master Core will start out in its Master Giant form. Setting the intensity to 6.0-7.4 (6.0-6.9 in Super Smash Bros. for Wii U) will have Master Core start as Master Beast. Finally, setting the intensity to 5.1-5.9 will have Master Core start as Master Edges.

Master Shadow is always fought after Master Edges, and it is a clone of the fighter, down to the fighter's customizations, which include any active equipment and custom specials. The clone begins as being larger than the fighter, but it shrinks as it takes damage. The player either has to KO Master Shadow or fully deplete its stamina to defeat it.

In the Wii U version, an exclusive form known as Master Fortress appears after beating the first four forms, but only when the intensity level is set to 8.0 or higher. The player is given 3 extra minutes, along with a Heart Container, and must travel though a maze made from the Swarm to destroy various weak points. Master Fortress only appears in Solo mode, however, so it is never encountered at all in Group mode.

Once the Swarm is defeated, the black mass disappears, and reveals Master Core's true form, a colorful ball resembling a Smash Ball. In this state, Master Core is completely vulnerable, though if it is not destroyed within 45 seconds, it rises and starts to attack the player by emitting waves that instantly KO the player if hit before it automatically self-destructs.

Master Giant
If the intensity of Classic mode is 7.0 (7.5 for the 3DS version) or above, Master Giant is the first form of Master Core. It has a wide variety of attacks, including the ability to physically lift up the stage in an attempt to hurt the player. When it takes enough damage, it loses its head, disabling some of its attacks.

Master Beast
Unlike the Master Giant, the Master Beast stays on-stage for most of its attack duration. It will appear first from intensities 6.0 to 6.9 (6.0 to 7.4 on the 3DS version), otherwise it will follow Master Giant at higher intensities, and not appear at all on lower intensities.

Master Edges
If the intensity is set from 5.1 to 5.9 in either of the two versions of the game, Master Edges is the first form of the Master Core that appears. All of the attacks from this form involve swinging the swords at the player.

Master Shadow
This form always follows Master Edges, no matter what the intensity is. The Master Shadow takes the form of the player, but bigger. It will copy everything right down to the custom moves and abilities. This form starts bigger than the character and gradually shrinks as it is attacked. When it is hit off the blast line or runs out of stamina, it will always transform into the true Master Core.

However, in Super Smash Bros. for Wii U, if the player is playing Solo Classic mode at intensity 8.0 or higher, he/she will be required to defeat Master Fortress next.

It should also be noted that in Group mode, Master Shadow will only copy the first player; the second player will never be copied.

Master Fortress
Master Fortress appears at intensities 8.0 or higher on the Wii U version, but only in Solo mode; this phase gets skipped completely in Group mode. When this appears, the player must trek through the fortress to destroy 4 cores. After destroying 2, the player is automatically ejected and must reenter. Inside the fortress are shadowy foes hoping to impede the player's progress, and danger zones much like the ones in The Great Cave Offensive. The danger zones will automatically KO above 100%.

Master Core
If Master Shadow is defeated, the true Master Core appears. It will not attack for most of the time. However, if it stays idle long enough, it will rise and attack with five waves, similar to Tabuu's Off-Waves, that automatically KO the player if they hit before it self-destructs.

In Super Smash Bros. for Wii U, if the player is playing Solo Classic mode at intensity 8.0 or higher, the true Master Core will appear after Master Fortress is defeated.

Super Smash Bros. for Nintendo 3DS / Wii U trophy
In Super Smash Bros. for Wii U, the trophy can be obtained by purchasing it at the Trophy Shop.

Trivia

 * In Master Core's battle theme, a series of beeps play that spell out its name when translated from.
 * There are unused artworks of Master Core's various forms in the files for Super Smash Bros. for Wii U. The artworks for Master Giant, Master Beast, Master Edges, and Master Core itself were later reused for their respective spirit in Super Smash Bros. Ultimate.