The Shadow is a Pureblood Heartless introduced in Kingdom Hearts. Although the Shadow is not the weakest type of Heartless, it is the most basic type, and it is still a threat to those without the Keyblade. It is found in each world in every game, excluding the worlds of Kingdom Hearts Birth by Sleep and Kingdom Hearts 3D: Dream Drop Distance; Atlantica in Kingdom Hearts, Kingdom Hearts: Chain of Memories, and Kingdom Hearts II; and The World That Never Was in Kingdom Hearts 358/2 Days. In Kingdom Hearts Birth by Sleep Final Mix, this Heartless appeared only in the Realm of Darkness during the Secret Episode of the game. Certain Heartless, such as the Darkside, the Dark Follower, or Ansem, Seeker of Darkness, can also summon Shadows, and the Shadows spawned by the Dark Follower are violet in coloration, rather than the traditional black.
A normal Shadow has a vaguely humanoid body structure. It has a round, spherical head with circular, glowing yellow eyes. It also has two long, twisted antennae sprouting out of the top of its head. Each of its hands has three clawed fingers, and its feet are large and lack any discernible digits. With the exception of its eyes, this Heartless's body is completely black (with the exception of the Shadows summoned by the Dark Follower, which are dark purple).
The Shadow's name is a reference to a shadow, highlighting its status as the most basic type of Heartless. The name could also be a reference to the Shadow's ability to flatten itself into a silhouette on the ground, and become a literal shadow.
Kingdom Hearts Birth by Sleep
While Aqua is traversing the Realm of Darkness, she encounters the Shadow among a few other Pureblood Heartless.
The Shadows first appear within Sora's Dive to the Heart, but are summarily destroyed by Sora, along with the Darkside, and he awakes from his dream. However, when Riku opens the door to Destiny Islands's heart, the Shadows reappear to devour the children's island. Sora notices the storm caused by their arrival and races to the island, but although he attacks them with his Wooden Sword, he is unable to damage the eldritch monsters until he discovers the Keyblade. Although he is now equipped to fight back the horde, his friends have already fallen into the darkness, and the island's heart has been devoured.
Shadows continue to appear as minor Heartless throughout the worlds, but do not reappear in force until Sora completes the Door to Darkness at Hollow Bastion by releasing Kairi's heart from his body. Not only does this change him into a Shadow, but the triumphant Ansem summons a swarm of Shadows to chase Kairi, Donald Duck, and Goofy from the castle. However, at the Entrance Hall, Kairi notices the Shadow that is Sora and embraces him, giving him back his human form.
Kingdom Hearts 358/2 Days
Shadows appear in the Mission Mode tutorial when the player learns about collecting Mission Points. They also appear when Roxas trains with Marluxia, Marluxia then proceeding to tell Roxas why the Organization ignored Pureblood Heartless, using the Shadow as an example. Much later in the storyline when Roxas went to Halloween Town on a mission in which he was to meet up with Xigbar, he was surrounded by Shadows before being rescued by the latter. Still later on, Roxas fought a more powerful version of the Darkside, the Dark Follower. The Dark Follower had the ability to summon purple-colored Shadows.
Kingdom Hearts: Chain of Memories
Several Shadows spawn when Sora and company attempt to leave the card world of Monstro, when Jack Skellington mentions a "problem" in Halloween Town, and when Sora arrives in Agrabah to find Aladdin under attack by Heartless.
Kingdom Hearts II
When Sora, Donald, and Goofy, as well as Kairi and Riku separately enter the Hall of Empty Melodies, a swarm of Shadows appears and attacks them. Riku lends Kairi a Keyblade, and they each fight back the swarm. However, it is Xigbar who finishes the Heartless off, before he challenges Sora to battle. After Ansem fires the Kingdom Hearts Encoder at Xemnas's artificial Kingdom Hearts, the shower of hearts that results attracts a gigantic swarm of Shadows, who attack the castle. Maleficent and Pete offer to hold off the Shadows so that Sora and his friends can defeat Xemnas, in exchange for the castle itself. When the castle is destroyed in Xemnas's final assault, it is assumed that the Shadows are as well.
Kingdom Hearts Manga
When Sora goes to check on the raft during the night of the storm, he spots Riku and Kairi's boats at the dock and rushes off to make sure they're safe, unaware of the Shadows beginning to emerge from the ground behind him.
Kingdom Hearts 3D: Dream Drop Distance
Multiple Shadows are shown in the trailer for Kingdom Hearts 3D: Dream Drop Distance. They appear before Sora in Traverse Town and surround him.
Kingdom Hearts III
Shadows live up to their name, emerging from the ground to attack with a simple but fierce claw strike. Although the Shadow is relatively easy to defeat when alone, its habit of attacking in swarms can make it too much to handle. If it is too much, it is a good idea to use Thunder (only in Kingdom Hearts) because it has a wide range. If it is alone, just fight it with the Keyblade.
Although Sora can block the Shadow's attacks, unlike with other Heartless, he will earn no Tech Points.