They have a centaur-like structure, and wield a large spear as their weapon.
- Slash Out: Rears up then swings weapon
- Thrust: Jabs weapon forward
- Assault: Rushing body blow
- Flourish: Windmill spin with weapon
- Explosion: Creates explosion in front
Getting close in can really take a chunk out of Sora and friends' HP, and can also take a large chunk out of your morale gauge during missions, so long-range magic is less dangerous. Although they have powerful attacks, they won't attack unless they are in range at the beginning of the battle or are provoked. These Heartless get especially fast when their HP gets low.
Earlier in the game, when you don't have too much in the way of abilities and/or Keyblades, keep a distance and pelt him with magic, preferably Thunder if available, or else use Blizzard. An alternative is to simply go to town with Valor Form, hammering the Assault Rider with as many combos as you can before reverting.
Later (i.e. the second time you arrive), use Master Form along with Wishing Lamp and Follow the Wind, attacking with combos and powerful magic such as Thundara/Thundaga and Blizzara/Blizzaga. When it starts getting a bit adventurous with its attacks, feel free to use a tier of Reflect if necessary.