Dark Hide

The Hunter of the Dark is a Heartless that can be found exclusively as a boss in Kingdom Hearts Birth by Sleep Final Mix. It is the final boss of the Secret episode and as such, is only faced by Aqua.

Kingdom Hearts Birth by Sleep
While making her way through the Valley of the Darkness in an attempt to return home, Aqua is stalked by the unseen Hunter of the Dark, as seen through the Heartless's bloodshot red vision. Upon moving in the shadows, Aqua notices the Heartless's presence, and draws the Master Keeper. The Heartless attacks from behind, knocking her down, but Aqua soon retaliates with a Fire spell, forcing it to back off to the shadows, showing Aqua nothing but its red eyes.

She quickly realizes that it's not an Unversed, and like the other creatures she's been facing, it is a denizen of the Realm of Darkness. She then engages the Hunter of the Dark in battle, and emerges victorious after a strenuous showdown. However, the fate of this creature is left unknown.

Appearance
The Hunter of the Dark has a massive purple body with dark magenta spikes running down its back, as well as a "mane" of dark magenta tentacles around its head. Its tail fades to a dark red tip and it sports four spikes, along with purple claws on each of its four legs. The most distinctive feature of the heartless is the red glow emitted by it's yellows eyes in the dark. The Heartless also sports a jagged mouth, blue markings on its face and body, and chains around its forelegs. Its body is rather long and thin and, despite its massive size, the Heartless moves rather quickly.

The Heartless is able to cloak itself and its surroundings in darkness, obscuring almost all of its features except for its glowing eyes, which shine bright red. The Heartless's eyes seem to be able to zoom in on what the Heartless is looking at, giving things a red tint. Glowing red veins are present around the sides of the Heartless's field of vision. The Heartless also frequently creates after-images of itself of various colors as it moves, including red, green, and purple.

The Hunter of the Dark looks similar to the Behemoths from the Final Fantasy series.

Trivia

 * The Hunter of the Dark still lacks an official name. The term "Hunter of the Dark" is based on the name of the battle music that plays when it is fought against. "Red Eyes", another popular fan-made name, is based on the bright, Unnamed Heartless.png that its eyes produce in the dark.