Darkside

Darkside is a boss from Kingdom Hearts. It is a colossal pureblood Heartless that Sora encountered 3/4 times. Instances included in the mysterious Awakening, the Destiny Islands, and in the End of the World. It also has a resemblence to Twilight Thorn which could possibly be its Nobody. Sora also glimpsed a number of Darksides within Kingdom Hearts before they were destroyed by King Mickey.

Darkside can spawn Shadows and its theme song is Destati. It has a heart-shaped hole in its stomach. It creates Shadows by creating an orb which it puts in the hole in its stomach. The monster can also fire these orbs from its stomach as offensive weapons. It's also the very first boss that is battled in the series.

In Kingdom Hearts, at the first battle with Darkside at Awakening, he has 240 HP, his Attack Power is 2, and his Defense Power is 2. Sora recovers no MP for hitting him (because he doesn't know any spells at the time), but he gets 18 EXP points for defeating him. Then, at the battle with Darkside at Destiny Islands, Darkside has 300 HP, his Attack Power and his Defense Power become 6. Sora recovers no MP for hitting him, because again, he knows no spells at the time, but he gets 60 EXP points for defeating him. At the last battle with Darkside at the End of the World, he has 900 HP, his Attack Power becomes 40 and his Defense Power becomes 30. Sora recovers 58 MP from hitting him, and gets 8,000 EXP points for defeating him.

One step down from a Darkside is Invisible.

You can also fight with a Darkside in Kingdom Hearts: Chain of Memories.

The Darkside will be a boss battle in Kingdom Hearts 358/2 Days.

Kingdom Hearts
''Enormous Heartless that appeared in Destiny Islands with Shadows. It led the Shadows in the battle against Sora when he first received the Keyblade. Although Sora defeated it, the island was swallowed by the darkness.''

Kingdom Hearts: Chain of Memories
The Heartless that attacked Sora's home, Destiny Islands.

Sora fought valiantly to protect the islands and his memories there.

Card
Darkside (Enemy Card)

Trivia
If you can climb Darkside's arm and attack his head, you get tech points for every combo finisher landed.