Barrel Spider

The Barrel Spider is an Emblem Heartless found in Kingdom Hearts and Kingdom Hearts: Chain of Memories.

Design
Simple and straightforward, the bodies of Barrel Spiders are composed of an ordinary wooden brown barrel, which enables them, when at rest, to blend in with environments that contain barrels. When a Barrel Spider is struck, four purple and pale pink legs that end in sharp talons burst from the sides; a fifth piece also chips away to reveal a sinister glowing yellow eye that allows whatever resides within the barrel to see where it is going. The Barrel Spider has a relative, the Pot Spider, with a similar appearance and behavior.

The Barrel Spider gets its name from resembling a wooden barrel with typical spider-like legs protruding from holes in the sides.

Strategy
Because of their explosive properties, it's best to avoid close range battles with them; and instead use Fire, or Blizzard magic on them. However, you can use their explosive properties to your advantage, to stun groups of enemies.
 * Kingdom Hearts

Before showing their true form as a heartless, attacking a suspected barrel with magic can reveal whether or not it is a Barrel Spider. If the barrel blows up, it is not a Barrel Spider, but if it doesn't, it is.

In Kingdom Hearts: Chain of Memories and its remake, Barrel Spiders pose as regular barrels until they are touched with the Keyblade. The best way to reveal them without going into battle mode is to compare them to other barrels, or alternatively, smash the barrels with an explosive barrel. Barrel Spiders are usually a little darker than regular barrels. In battle, Barrel Spiders use cards numbered 4 to self-detonate. It's best to card break their cards immediately, so that they don't get the chance to explode, taking away the chance to earn Experience.
 * Kingdom Hearts: Chain of Memories