Shadow

A Shadow is a Pureblood Heartless which appears in Kingdom Hearts, Kingdom Hearts: Chain of Memories, and Kingdom Hearts II. It has also been seen in screenshots of the upcoming game, Kingdom Hearts 358/2 Days.

Shadows are the weakest and most common of all Heartless. They are Pure Heartless found almost anywhere, though their hot spots include the Destiny Islands, Traverse Town, Wonderland, End of the World, and The World That Never Was. Shadows are created when the darkness in an ordinary person's heart is unleashed. Other pure Heartless, like Darkside, can produce Shadows or at the very least, summon existing ones.

Despite their weak appearance, they are a threat to regular people as they usually have no way of defending themselves. Even Sora had no means of defeating them, until he attained the Keyblade, since without it he can't inflict any noticeable damage to them.

There is a higher "class" of Shadows called Neoshadows, who are far more organized and dangerous. Shadows also have Nobody counterparts called Creepers.

Kingdom Hearts
''Heartless that emerge from various places. They sneak up to their enemies and strike them with sharp claws. They are extremely tenacious, often chasing their prey to the end.''

Kingdom Hearts: Chain of Memories
A Heartless that pops up in all kinds of places.

''The Shadow ambles around and attacks without warning. It is completely invulnerable while hiding within the darkness.''

Kingdom Hearts II
It sinks into the ground while moving, so timing is the key to defeating it.

The moment it surfaces, attack away!

Kingdom Hearts

 * Awakening
 * Destiny Islands
 * Traverse Town
 * Wonderland
 * Deep Jungle
 * Olympus Coliseum
 * Agrabah
 * Monstro
 * Halloween Town
 * Neverland
 * Hollow Bastion
 * End of the World

Kingdom Hearts: Chain of Memories

 * Traverse Town
 * Agrabah
 * Olympus Coliseum
 * Wonderland
 * Monstro
 * Halloween Town
 * Neverland
 * Hollow Bastion
 * Twilight Town
 * Destiny Islands
 * Castle Oblivion

Kingdom Hearts 358/2 Days

 * Twilight Town
 * Wonderland
 * Olympus Coliseum
 * Agrabah
 * Beast's Castle
 * Halloween Town

Kingdom Hearts II

 * Twilight Town
 * Hollow Bastion/Radiant Garden
 * The Land of Dragons
 * Beast's Castle
 * Underworld
 * Disney Castle
 * Timeless River
 * Port Royal
 * Agrabah
 * Halloween Town
 * Pride Lands
 * The World That Never Was

Abilities
A Shadow's primary and most useful ability (from its perspective) is the ability to sink into the ground and act as a real shadow. In this state, Shadows cannot be harmed. A Shadow's most often used melee attack is a lunge-and-scratch attack, when a Shadow leaps into the air, directly at its opponent, scratching wildly in front of it.

Trivia

 * In Kingdom Hearts, Sora turns into a shadow after using Ansem's Dark Keyblade to unlock and free Kairi's heart at the cost of his own. When in this form, Sora can only move and jump. This is the only time you can play as a Heartless.
 * In the regular Chain of Memories, Atlantica is the only world with Heartless, but without Shadows. In Re: Chain of Memories, Shadows are available in Atlantica only if a Bottomless Darkness map card is used.
 * Shadows may possibly be based upon the similarly named enemy from Super Mario RPG, also developed by Square.
 * Shadows are arguably the weakest enemy in the series.