Demon Tide

The Demon Tide is a Pureblood Heartless that appears in Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-. It is a more powerful version of the Demon Tower that ambushes Aqua and King Mickey in the remains of Destiny Islands.

Story
The Demon Tide attacks Aqua and King Mickey when they arrive at the remains of Destiny Islands and investigate the door inside the Secret Place. It is defeated by the two Keyblade Masters, but it returns to hunt Riku shortly after they find the Kingdom Key D behind the door. Aqua and King Mickey rush to Riku's aid, and Aqua attempts to restrain the Demon Tide with chains of light. The Heartless breaks free, and it drags Aqua back to the remains of Destiny Islands, destroying Mickey's shirt in the process. As Mickey helps Sora and Riku seal the Door to Darkness, Aqua battles the Demon Tide and promises to help anyone else who falls into the Realm of Darkness.

Kingdom Hearts III
Sora battles the Demon Tide in a teaser trailer for Kingdom Hearts III that was released at E3 2013. He faces the boss in Twilight Town's Tram Common.

Design
Much like the Demon Tower, the Demon Tide is a swarm of Shadows. It is large, travels in waves, and has a core that glows violet or orange.

Strategy
The Demon Tide is the final boss of Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-. As such, it is resilient. Aqua should be sure to have many items equipped before she faces this Heartless.

Phase one
This boss initially has access to three attacks: a soaring strike, a Shadow trap, and an assault from underground. Each of these can be avoided with a well-timed Barrier, and a quick Counter Blast can then be used to damage the boss. Aqua can tell when the Demon Tide is about to attack by watching the eyes of the Shadows that comprise it: when the eyes glow red, it means the boss is about to strike. Aqua should avoid the Demon Tide in these instances and use a combination of physical attacks and magic to harm it in the interim. Whenever the Wayfinder Situation Command becomes available, Aqua can use it to immobilize the Demon Tide and quickly deplete its HP by teaming up with King Mickey.

Phase two
The Demon Tide becomes much more aggressive in an attempt to protect its vulnerable core. Added to its arsenal is a new projectile attack that is best avoided with Cartwheel. Aqua should bombard the Demon Tide with aerial combos until its HP is fully depleted.