Iron Imprisoner

The Iron Prisoner (アイアンプリズナー) is an Unversed that is found in Kingdom Hearts Birth by Sleep. Although it is a boss, it only appears at Mirage Arena. When it is first fought, it is chained and imprisoned in a gibbet, but it gradually releases itself over the course of its battles. The four forms it takes are known as Iron Prisoner I, Iron Prisoner II, Iron Prisoner III, and Iron Prisoner IV.

Design
The Iron Prisoner is a large, armored Unversed with four different forms. In its first form, the Iron Prisoner I's lower body is locked in a black gibbet with silver highlights and several black, diamond-shaped gems set in it. Its arms, which are covered in black armor with two blue gauntlets, are bound by four red chains. Only its head, encased in a helmet that is light grey on its right half and grey on its left half, is free to move. It has jagged, black horns on either side of its helmet, though they are not of the same shape. The right horn is somewhat straighter and more horizontal, while the left horn hooks upward sharply. Its eyes are red, set in an angry expression, and slightly uneven.

The Iron Prisoner II is identical to its first form, save for two significant changes. The Iron Prisoner's chains are gone and its arms are free, making its gauntlets and red collar clearer. It is also now wielding a large, red and black hammer with spikes on its head. The handle of this hammer is tan and the pommel is a black spike. The head of the hammer can conjure fire.

The Iron Prisoner III is now free of its gibbet, exposing its grey legs. Both of its feet sport black bands with blue highlights on them. Its collar is much smaller and the grey breastplate it wears is now clearly visible.

The Iron Prisoner IV sports a radically different coloration than its previous incarnations. Its armor is now much darker, mostly colored in shades of black and dark grey. Its lower legs are light grey and the tips of its feet are red. Its gauntlets are now red and black, and its breastplate sports blue highlights. The Iron Prisoner’s helmet is now uniformly colored black and its eyes have changed shape, though they are still set in an angry expression.

Abilities
The Iron Prisoner is one of the strongest Unversed bosses in the game. It wields its giant hammer in battle, and the element of fire to enhance its attacks. It can erupt out of the ground with the force of a geyser. It can also entrap players in cages leaving players at its mercy. It can also spin around the arena while coated in a fiery aura, burning players on contact. In its first and second form it can shoot lasers from the bottom of the gibbet to burn players. In its fourth form it can suck players in to deal damage, and possess the room turning it red and causing the tiles to fly off and attack players. It mainly moves around the arena by levitating or teleporting.

Strategy
The Iron Prisoner is one of the most powerful bosses in the game, second only to Vanitas's Sentiment. Therefore it is recommended the player be at a high level, have the Ultima Weapon keyblade, and have the strongest Shoot Lock available: Ultima Cannon for Terra, Shiny Bloom for Aqua, and Pulse Bomb for Ventus. The strategies for each form are below.

Iron Prisoner I
In its first form, it's chained and trapped in a gibbet. It attacks mainly by swinging the gibbet at you or spinning around like a fiery tornado. It can also entrap you in a cage or erupt out of the ground like a volcano. The best way to start the battle is to use your Shoot Lock to shave away at its HP bar, then attack normally. Beware when its HP is low. It shoots lasers from the bottom of its gibbet, dealing fire damage on impact. But overall, it is the easiest of the four forms. Merely dodge the lasers and attack.

Iron Prisoner II
In its second form, nothing much has changed except for the fact it now uses its massive hammer to deal large damage. It can also spin with the hammer outstretched, dealing fire damage on contact. otherwise, it retains all of its attacks from its first form. so simply dodge, attack and use Shoot Locks when possible.

Iron Prisoner III
Its third form is the same as its previous two incarnations. With the only obvious difference that its legs are no longer bound in a gibbet. It is now faster than the other two forms, but it cannot shoot lasers. It retains its other moves so the strategy is the same.

Iron Prisoner IV
The boss's final form, and its most powerful one yet. It retains its old moves with some new ones. The cage it traps you with is now on fire and will damage you on contact. It also has an attack where it sucks you in close before releasing a large explosion. When its HP is low it will possess the room, turning it red and causing the tiles to fly off and attack.

Etymology
The former part of the boss' name resembles its metallic appearance, while the latter part represents how it is chained and imprisoned in a gibbet.