Antiform

Antiform is a Drive Form which appears in Kingdom Hearts II. It uses both party members, and consumes all of Sora's Drive Bars. It represents the darkness that still dwells within Sora's heart, and it is obtained along with Sora's new clothes at Mysterious Tower. Its emblem is a black, demonic silhouette.

Design
Antiform is strongly reminiscent of the AntiSora Heartless from ', and Tetsuya Nomura has confirmed in an interview with ' that Sora's ability to enter this form is due to his transformation into a Shadow. Specifically, Sora's Antiform has more feral behavior, in that it runs about on all fours, and instead of using the Keyblade in this form, Sora attacks with claws on his hands. In addition, when hanging onto a ledge, Sora's AntiForm clings with one foot, rather than one hand. Aesthetically, Sora's skin and hair become ink black, his eyes glow yellow like a Heartless's, and his clothes become black with blue accents. Furthermore, he constantly emits darkness from his arms and back in the form of misty black and violet wisps.

Mechanics
Unlike other Drive Forms, Antiform cannot be purposefully activated. Instead, it will be randomly activated when Sora attempts to enter Valor Form, Wisdom Form, Limit Form, or Master Form while in combat, based on a hidden "Anti Point" counter. This counter is increased by 1 every time Valor, Wisdom, Limit, or Master Form is activated, but is reduced by 10 when Final Form is used. Gameplay-wise, Antiform exists as a consequence of abusing the Drive system, and it is meant to be "strong but troublesome". However, the Two Become One Keyblade's Light & Darkness ability will make it so only Antiform or Final Form activates when a Drive Form is used. Antiform starts at having a 75% chance of being the activated form when a Drive Form is used in this state, but this percentage goes down to 50% and then 0% until Final Form is obtained. It is also impossible for Sora to enter Antiform while an unconscious ally is on the field, or if he is trying to change to Final Form. Antiform can only be manually deactivated outside of battle, though its Drive Gauge caps out at 6, and consuming Drive Orbs will actually cause the gauge to deplete faster. In addition, though Drive Forms normally persist through cutscenes and Cup seeds, Antiform will instead revert to Standard Form.

Like Valor Form, Antiform cannot use magic; in fact, it cannot use any commands beyond "Attack" and "Revert." Furthermore, Sora cannot pick up HP Balls while in Antiform, meaning he is completely unable to heal in any way. Although Sora moves at twice his normal speed while in Antiform, he takes 50% more damage from attacks, and he does not gain experience from defeated enemies.

Strategy
When using Antiform, lacking any method of healing means that the player's main goal will be to evade the enemies. Although Antiform's high speed and Anti Glide ability make it easy to stay safe through simply evading the enemy's attacks, its quick combos will often let it keep an enemy stunned while also dealing damage, and can also deflect many attacks automatically. Furthermore, several of Antiform's attacks have a neutral or dark attribute, allowing them to break through enemies which are immune to the weapon-attribute, like the Large Body.

Unlike other Forms, Antiform automatically reverts to Standard Form when Sora moves to another room, emptying the Drive Gauge. However, if the room is a World Exit or one where party members are walking around, it will refill as normal. Because of this, the Brink of Despair can be used to easily recharge the Drive Gauge immediately after defeating Roxas, allowing the player to repeatedly activate Drive Forms with Light & Dark equipped in order to unlock Final Form.