Demon Tide

The Demon Tide is the final boss of 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.

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.