A Core Blox is a Pureblood Heartless found exclusively in Kingdom Hearts Re:coded. Core Blox are found in System Sectors and Keyholes. The Heartless bosses within each Keyhole are made from a Core Blox, and the final floor of each sector in Hollow Bastion part II contains a Core Blox. Three appear together in a System Sector in Agrabah.
It appears as a purple colored block with light purple colored, jagged cracks. When struck the color changes to red with yellow colored cracks, making it resemble a Blast Blox. It creates a long body made up of the other Blox in the game which periodically change throughout the battle.
Core Blox are reasonably difficult enemies in the earlier part of the game if you don't use proper strategy. The best way to defeat them is to let it come past you, and then you can take out its body, without sustaining much damage. Once you have destroyed its body, it will stop moving, and you can unleash up to four combos on it, dealing a good amount of damage. Core Blox also take decent damage from commands, but make sure not to use a command that takes a lot of time to execute, otherwise you will waste valuable time, where you could damage it more by attacking or with quick commands.
After a certain amount of time, it will regenerate its body and it will start moving again. Keep repeating this process until it falls. Sometimes, the Core Blox will transform its body into different types of Blox, but when it transforms its body into Blast Blox, touch its body and the resulting explosion will destroy all of its body and deal a good amount of damage.
Often, the Core Blox will spawn Danger Blox for a body, preventing Data-Sora from physically attacking them. A good way to destroy these blocks quickly is when most of its body is coiled around you, use a magic command that hits a large range around Data-Sora, such as Thundaga. It would be useful to note, Mega Flare deals a great amount of damage to the Core Blox when it hits, and even though you don't get Mega Flare until later in the game, it can make this fight a lot easier. Even though Mega Flare is useful, it's also good to note Mega Flare does not destroy the blocks on its body, no matter what type, so it's good to only use it when you've got a clear shot at hitting the Core Blox and not its body parts.