Demon Tower

The Demon Tower is a Pureblood Heartless that appears in Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage- and Kingdom Hearts III. It is a gathering of Shadows that take on the form of large twister.

Kingdom Hearts III
A dark swarm of Shadows, stacked into a looming spire.

The fact that its foul ilk has been seen not just in the realm of darkness but in the realm of light is surely a harbinger of some coming evil.

Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-
Aqua first encounters a Demon Tower after finding the five gears in the Castle of Dreams remnants, and defeats it in battle. She later encounters another one after being reunited with Mickey in the Depths of Darkness, and the two are able to defeat it together.