Antiform

Anti Form 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 is obtained along with Sora's new clothes at Mysterious Tower. Its emblem is a black demonic silhouette.

Mechanics
Unlike other Drive Forms, Anti Form cannot be purposefully activated. Instead, it will be randomly activated when Sora attempts to enter Valor, Wisdom, or Master Form, based on a hidden "Anti Point" counter. This counter is increased by 1 every time Valor, Wisdom, or Master Form is activated, but is reduced by 10 when Final Form is used. Gameplay-wise, the Anti Form exists as a consequence of abusing the Drive system, and is meant to be "strong but troublesome". However, the counter system is ignored while the Two Become One Keyblade is equipped, as its Light & Dark ability will make it so only Anti Form or Final Form activate when Form is used. Anti Form starts at having a 75% chance of being the activated form when Form is used in this state, but goes down to 50% and then 0%, until Final Form is obtained. It is also impossible for Sora to enter Anti Form while an unconscious ally is on the field, or if he was trying to change to Final Form. Anti Form 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 be consumed faster. In addition, though Drive Forms normally persist through cutscenes and Cup seeds, Anti Form will instead revert back to Standard Form.

Unlike the other Growth Abilities, Anti Form's "Anti Glide" ability cannot be leveled and is thus inaccessible in Standard Form. Like Valor Form, Anti Form cannot use magic; in fact, it cannot use any commands beyond "Attack" and "Return to normal". Furthermore, Sora cannot pick up HP Balls while in Anti Form, meaning he is completely unable to heal in any way. Although Sora moves at twice his normal speed while in Anti Form, he takes 50% more damage from attacks, and doesn't gain experience from defeated enemies.

Strategy
When using Anti Form, the lack of any method of healing means that the player's main goal will be to evade the enemies. Although Anti Form'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 Anti Form'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.