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 fully-powered version of the Demon Tower that ambushes Aqua and Mickey at the remains of Destiny Islands.

Story
When Aqua and Mickey arrive at the remains of Destiny Islands, she recalls the last time she visited the Islands and met Sora and Riku. Mickey explains that the two boys have been aiding him in his journey and prepares to investigate the door leading to the Secret Place. However, the Demon Tide attacks, forcing the two Keyblade Masters to battle it in a strenuous battle.

Later, after Mickey acquires the Kingdom Key D, he and Aqua notice Riku rushing to the Door to Darkness and prepare to help him seal it. Unknown to Riku, though, the Demon Tide reappears and attempts to attack him. The two Keyblade Masters rush to Riku's aid, with Aqua attempting to restrain the Demon Tide with chains of light. The Demon Tide breaks free and drags Aqua back to the remains of Destiny Islands, destroying Mickey's shirt in the process.

Inside the remains of Destiny Islands, Aqua continues to fight the Demon Tide as she silently promises to help anyone else who falls into the Realm of Darkness.

Appearance
The Demon Tide, much like the Demon Tower, is comprised of a swarm of Shadows. Unlike the Demon Tower, the Demon Tide is bigger, is wave-shaped (hence the name, "Demon Tide"), and has a core at the tip of the Heartless that glows either violet or orange.

Strategy
The Demon Tide is the final boss of the game, and as such, is very resilient with 13 health bars. To prepare for this boss, Aqua needs to keep her item bar packed with Hi-Potions, Mega-Ethers, and even Elixirs or Megalixirs if one knows how to find them.

At the start of the fight, the Demon Tide has three attacks, all telegraphed by the Shadows' eyes glowing red. The first consists of it ramming Aqua and Mickey, a manner reminiscent of the Demon Tower. Simply use Barrier to guard the hits. It can also cough up Shadows, again like the Demon Tower, but don't be fooled by the Shadows- they can trap Aqua in a swarming combo if ignored. To evade the Shadows, use Barrier to ward them off, or Cartwheel away. At this point, attacking the Tide is not a wise idea because of its eyes. The third consists of it burrowing underground, its presence indicated by a cloud of dust. When it emerges, use Barrier and Counter Blast to deliver some damage.

As usual, use Keyblade combos and magic to whale on the Demon Tide whenever the Shadows' eyes are yellow. While its core is its weak point, hitting the Shadows comprising the being also counts as damage to the boss.

At random points, Mickey can hop on to the Demon Tide, prompting the Wayfinder Situation Command. During this period of time, the Demon Tide is vulnerable, so take advantage of this point to whale on the boss. When this command is activated, Mickey scatters the Demon Tide's Shadows, followed by Aqua binding the boss's core. Immediately afterwards, the Wayfinder Style Change activates. Use the period of time to unleash it on the core, but be cautious to use all the time given- after the Wayfinder finisher, the Demon Tide breaks free, reassembling its Shadows in the process.

After the boss's health hits a certain point, it burrows underground, triggering the second phase of the fight. The Shadows now surround the core in a twister formation. During this time, the Tide retains its ability to summon Shadows, but it also has a new attack in which its core rises upwards and fires globs of darkness that home in on Aqua, with Cartwheeling being the prime way of avoiding it. After some time, the Tide launches Aqua into the air, firing the globs from underground. Gravity can pull Aqua to the boss, but try to remain airborne by using Combo Master (or other methods if on Critical Mode).

When the attack is over, the Demon Tide is now vulnerable. Again, use Keyblade combos and magic to fell the boss. With patience, the Tide will fall.

If having trouble with the second phase, when the Demon Tide is chained, fire two Shotlocks at the core, consuming Elixirs to restore the Focus Gauge before firing two more volleys. Then use Wayfinder to deplete the rest of the boss's health to 1 HP. Only when the Demon Tide breaks free can it enter the second phase. Immediately afterwards, fire a spell at the core, defeating the boss once and for all.

Kingdom Hearts III
In the E3 2013 trailer, the Demon Tide attacks Sora in Twilight Town, with Sora leaping onto the massive Heartless and back onto the rooftops before engaging it in battle.