In Kingdom Hearts II, there are a lot of new features over the prior two games. One of these is the incredibly useful drive form set. These forms are all very different from each other but each has a few things in common. They can each reach a maximum of level 7, however you cannot exceed the level of your drive gauge, which is necessary to activate these forms. Each has a special ability, which can be obtained and leveled up by leveling the drive form. These are obtained at level 1 for each drive form, but for Sora to have them outside of drive the player must get the drive form up to level 3, at which point the form will bear the level 2 version of the skill and Sora will bear the level 1 version. There is also a glitch where the Drive Gauge will fill completely if the player does something that forces a reversion, such as exiting the world or entering a room where party members are roaming around loosely. Now, onto the drive forms themselves.
The first form you will be getting is Valor, which is obtained shortly after the tutorial with Roxas, in Yen Sid's tower. You obtain this alongside the Starseeker keyblade. The form turns Sora's outfit red, with a fleur de lis as a mark on various parts of the outfit. The drive form's special ability is high jump, increasing the jump height. Valor Form possesses Synch Blade, allowing Sora to use two keyblades while in the form. The focus of Valor is speed and strength, with Sora striking quickly. At this point square can be pressed to go instantly into a finisher so long as a basic combo has been initiated. Alternative skills include to copies of Combo Plus, increasing Sora's ground combo. The form levels up with every hit dealt while in it, and a good place to grind it in KH2FM is the Mushroom XIII challenge in Agrabah. This form costs three points on the Drive Gauge and consumes Goofy.
The next form is Wisdom Form, obtained alongside the keyblade Monochrome upon completing the Timeless River. This form changes Sora's outfit to blue and adds flame decals to some parts of the outfit. Its special ability is a dash, good for getting away from attacks. The focus of this form is magic, and Sora will gain new magical finishers and abilities for each magic type and the base attack being replaced by a magical projectile. Other skills obtained through Wisdom Form are MP Rage, adding MP and reducing MP cooldown for every hit taken by Sora, scaling to the damage taken, and MP Haste, speeding up the rate at which the MP cooldown occurs. Wisdom Form levels from killing Heartless. This form consumes Donald and three drive points.
The next form obtained is Master Form, obtained upon meeting up with Mickey on Hollow Bastion, upon looking for the password for Tron in Space Paranoids. The form turns Sora's outfit yellow with a stylized cross as its mark. The special ability of Master Form is Air Dodge, a double jump that boosts Sora in the direction he's moving as well as into the air. It can also be used with Final Form's Glide to produce an unusually fast glide with no acceleration time, and also deflects projectiles. Master possesses Synch Blade again. The focus of Master Form appears to be a mix of physical and magical attacks, but ground combos are impossible while using it. Magic can be cast infinitely with no finisher in this form. It is leveled up by collecting drive orbs. The best way to grind this is to equip the Sweet Memories keyblade from the Hundred Acre Wood and go to the Wizard's Tower later in the game, where you will find Gambler Nobodies. Playing their game with triangle will allow you to gain an abundance of munny if you succeed, which will become drive orbs thanks to Drive Converter. In KH2FM you can also kill enemies in the Cavern of Remembrance. The abilities granted by this are both air combo plus, increasing the air combo by one each. This form consumes Donald and Goofy, and costs four drive gauge points.
Exclusive to the Kingdom Hearts 2 Final Mix, Limit form can be obtained upon completing the second visit to Twilight Town and unlocking the Keyhole. This form makes Sora's outfit closely resemble his Kingdom Hearts 1 version, but with a crown mark in various points. Its special ability is Dodge Roll, which is incredible useful for its invincibility frames. The focus of this form is different from all others in that, rather than focusing on a combat type or damage type, it replicates numerous abilities from Kingdom Hearts 1, and it replaces magic with Limits, which are also from Kingdom Hearts 1 and are enhanced by using the Triangle prompt. Other abilities gained by Limit Form are Lucky Lucky, which increases the rate at which enemies drop certain updates, and Draw, which pulls in orbs from a larger range. Limit Form is leveled up by the limits it gains, and is best leveled at Agrabah's Mushroom XIII. It consumes no allies and four drive gauge points, and cannot trigger antiform.
As you've used Drive Forms the you may encounter Antiform. This drive form turns Sora entirely black with glowing yellow eyes, like a heartless, and the design of a dragon can be seen on the outfit. This form can be triggered at any moment when activating Valor, Wisdom, or Master form, and is more likely to trigger the longer it goes unused. It has no keyblades and no growth abilities, and seems to take more damage from enemies. Its upside is that it's fast and can deal a lot of damage, though the attacks blend into each other. This form will always consume all drive gauges and both Donald and Goofy.
The last form the player can get is, fittingly named, Final Form, obtained randomly when activating Antiform after defeating Roxas in the World that Never Was. It can most easily be obtained in KH2FM, where defeating Roxas gives the Two Become One keyblade, which makes Antiform always trigger. This form turns Sora's outfit white and adds a swirl image to parts of Sora's outfit. Its special ability is Glide. The form is easily one of the best in the game, as Sora will send his keyblades out to damage enemies from afar, doing good damage at a good rate, all the while bearing upgrades to his magical finishers, along with Synch Blade. Its combo attacks blend into eachother, much like Antiform. In fact, certain attacks even closely resemble Antiform, putting on display the correlation between Sora's dark and his light. Other abilities from Limit Form are entirely Form Boosts, allowing Drive Forms to go on longer. It's leveled up by killing Nobodies, which is best done in the World that Never Was. This form resets Antiform's chance of happening to its base.
It's a good idea to use Drive Forms often throughout the game, as the abilities gained from them are incredibly useful and can make many boss fights, such as Sephiroth, much easier.