The Armor of the Master is a data simulation of Master Eraqus, found exclusively as a boss in Kingdom Hearts Birth by Sleep Final Mix. As a data simulation, it has a likeness of Master Eraqus and dons his Keyblade Armor as well as uses his Keyblade, the Master Keeper.
The Armor of the Master is a sentient suit of Keyblade Armor that wields Master Eraqus's Keyblade in battle. Its torso is covered of dull, faded green armor and sports a small Mark of Mastery symbol in its center. The rest of the armor on its arms, legs, and chest are predominantly bronze and silver. Its pointed, armored boots are black and gold and its upper arms and thighs have wide, supplementary armor with gold edges covering them.
The Armor of the Master's helmet is silver with a gold chin with jagged "teeth" and a Mark of Mastery symbol of the same color adorning its forehead. The helmet is also decorated by three long, thin, silver pikes on its top and sides. Its hands and neck are covered by a black material.
As the boss is a simulation of Master Eraqus, it will utilize some, if not all, of Master Eraqus's attacks as well as a few light-based attacks of its own. The Armor of the Master can perform a long powerful combo with its Keyblade, throwing the player into the air during the combo and using a different combo finisher depending on the character being played; as Terra, the boss will perform a series of downward slashes that create shockwaves, knocking the player upward and leaving them up for more damage; as Ven, the boss will perform flying slashes similar to Air Drive; as Aqua, the boss will perform a Barrier Surge-like attack and finish with a slow moving magic bubble.
It is advised to block the boss's attacks and counter with a Reprisal to damage the boss and gain invincibility. The boss can perform Eraqus's Sonic Blade-like attack, shoot magical orbs that home in on the player if not deflected, and several magical blades that will seek out the player; both projectiles can be deflected back to the boss to damage it.
The boss can create magical blades to its will, periodically ensnare the player in chains of light, and if successful, will gain a seal on its back and changing many of its attacks. Its Sonic Blade-like attack will be changed to resemble an Iaido-style technique, inflicting many hits and its basic Keyblade combo will be quicker and may ensnare the player in a seal, lifting up the player and slamming the player back into the ground with a downward slash, similar to Marluxia's Flower Storm in Kingdom Hearts Re:Chain of Memories.
It can use the seal to stun the player as a counter-attack, leaving him or her open to more attacks. Like Master Eraqus, the boss will create five fiery pillars which will follow the player around before disappearing.It can create rotating lasers of light, but will constantly move the lasers up and down, making them difficult to dodge; the player can avoid damage completely by moving to the far reaches of the arena. Apart from that, depending on the character (Terra, Ven, or Aqua) you are playing as, the boss will use a different Command Style and its desperation moves will change each time it ensnares the player with the chains, switching between the seal, and the Command Style.
If played with Terra, it will use Critical Impact and its desperation move uses its light chains to bind Terra and pull a large chunk of the arena up and shoot it with a powerful blast of light. This attack requires the player to continuously press to break free of the chains binding Terra and perform a dash at the right moment to avoid the resulting explosion of the attack.
When played with Aqua, the boss will battle you with Spell Weaver and the desperation move will be to create large, spinning lines of light of different colors that will go around all over the field, with each one causing a different Status Effect. The player should dodge the attacks by Cartwheeling continuously until it ends.
Finally if the player uses Ventus to battle the boss, the boss will use Fever Pitch and will create three large, slow-moving tornadoes with its chains as the desperation move. In this case, the player should stay as far away from the tornadoes and the boss until the attack ends.
All of the boss's Command Styles are a faster version than the ones used by the characters and all the desperation moves can be predicted as the boss will fly into the air. Using Mine commands, as well as dark-based commands can help in defeating the boss. Dodging, Blocking, using Reprisals, and Shotlocks are critical in avoiding its attacks and damaging it. Commands like Unison Rush can be used to avoid its desperation move.
The Armor of the Master is a powerful user of the Keyblade and Magic. It can perform a powerful melee combo with its weapon capable of throwing the player into the air and also a high-speed iado-style technique that it follows with Collision Magnet. In terms of magic, the Armor of the Master can fire a rotating wheel of lasers, homing magical orbs and blades and create 5 gigantic homing pillars of fire. It also can fire chains of light capable of allowing the Armor to use unique and much more deadlier version of the player's attacks: with Terra, it can use a series of downward slashes capable of creating earthquakes and use it's light chains to bind him and raise a large chunk of the ground before firing a beam of light. With Aqua, it casts a barrier around itself, performs some spiraling slashes, and unleashes a slow bubble as the finisher, protects himself with a barrier while homing itself at Aqua and creates large, spinning lines of multicolored light that span the field and inflicts status effects on contact. With Ventus, it uses flying slashes capable of launching him to the air, reversal if attacked to counter with a slash from behind and creates two large tornados.
- The music that plays during the battle with the Armor is "Master, Tell Me The Truth", a remix of the Land of Departure battle theme "Future Masters".