Here is a list of Heartless that can be encountered:
Air Pirate- A flying Heartless that resides in the Pirate ship region of Neverland. They attack with dive bombs and punch attacks.
Air Soldier- A flying Heartless that appears in Traverse Town and some of the earlier worlds. They attack with high-flying kicks.
Angel Star- A slightly divine Heartless that appears in The End of the World. They attack with various magical attacks.
Aqua Tank- A large fish-like Heartless that appears only in Atlantica. It is usually coupled with 2-3 Screwdriver Heartless. It becomes temporarily invulnerable when hit by lightning attacks and attacks with a charge attack.
Bandit- A quick Heartless that appears in Agrabah. They attack with a curved sword and a spinning attack.
Barrel Spider- A Heartless that hides inside a barrel on Captain Hook's pirate ship. They become active when approached and explode on contact.
Battleship- A Heartless that has fused with a pirate ship. It appears on Captain Hook's pirate ship. They attack with cannonballs and homing missiles.
Behemoth- A giant bull-like Heartless. It attacks with stomps and an energy attack with its horn.
Black Fungus- A stronger version and fiercer version of the White Mushroom Heartless. It attacks with poison and turns stone to become temporarily invulnerable.
Blue Rhasody- A bell-shaped Heartless that attacks with Blizzard.
Bouncywild- A nimble monkey-like Heartless that bounces and runs around wildly. It attacks by dropping banana peels and using a slingshot from afar.
Creeper Plant- A plant-like Heartless that can sprout up from anywhere in the ground. It attacks by using its roots.
Crescendo- A hopping horn-like Heartless that does very little attacking.
Darkball- An eerie Heartless that moves erratically to attack.
Darkside- A large Heartless that first appeared in Sora's dream. It attacks with punches and an energy attack from its chest.
Defender- A large Heartless that uses a living shield. The shield attacks with either a Blizzard, Fire, or bite attack, while the user uses a spin attack.
Fat Bandit- A large Heartless that appears in Agrabah. It attacks by throwing its weight around and breathing fire.
Gargoyle- A dark Heartless that appears in Halloween Town. It attacks with dive bombs and a breath attack.
Green Requiem- A bell-like Heartless that casts Cure on any surrounding Heartless.
Invisible- A demonic Heartless that appears in The End of the World. It attacks with a large sword and a dark spell.
Large Body- a large Heartless that attacks by throwing its weight around. It is angered when attacked from behind, its only weak spot.
Neoshadow- A stronger version of the common Shadow Heartless. It can easily move through the shadows to attack.
Pirate- A Heartless that appears on Captain Hook's ship. It attacks with a large sword.
Pot Spider- A Heartless that hits in a pot. It appears in Agrabah and joins with other Pot Spiders to form Pot Centipede.
Powerwild- A monkey-like Heartless that attacks with slides and scratch attacks.
Rare Truffle- A docile, blue colored Mushroom Heartless that likes to jump. Keeping it in the air may be benefial to you.
Red Nocturne- A red bell-like Heartless that attacks with Fire and a charge attack.
Screwdriver- an aquatic Heartless that tags along with the Aqua Tank. It attacks with a harpoon and charge attack.
Sea Neon- An aquatic octopus-like Heartless. It attacks with its tentacles and spawns from Sheltering Zone Heartless.
Search Ghost- An eerie Heartless that drifts around aimlessly. It vanishes after a while.
Shadow- The basic and most common Heartless. It appears everywhere and is the weakest of the Heartless.
Sheltering Zone- An aquatic Heartless that drifts around the waters of Atlantica. It splits into several Sea Neons if not defeated quickly.
Soldier- The second most common Heartless. It attacks wildly with kicks and spins.
Tornado Step- a small, long-armed Heartless that jumps and spins constantly.
White Mushroom- a docile Heartless that could bring good fortune to those who help it.
Wight Knight- A mummified Heartless that attacks with its long arms and legs.
Wizard- A magical Heartless that has mastered several spells. It teleports around the battlefield to dodge attacks.
Wyvern- A dragon-like Heartless that attacks with its claws and dive bombs from high above.
Yellow Opera- A yellow bell-like Heartless that attacks with Thunder and a charge attack.