Flame Core

The Flame Core is a Pureblood Heartless that was introduced in Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-.

Kingdom Hearts III

 * Fire Blow (ファイアブロー)
 * Fire Throw (ファイアスロー)
 * Rush (突進)
 * Meteor Attack (メテオ攻撃)

Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage
Attacking it with melee attacks works to wear down its HP, but at that point it lights itself completely ablaze and charges around, damaging Aqua. Three shots of Blizzaga can slay a Flame Core without much trouble.

Kingdom Hearts III
Flame Cores behave similarly to 0.2. Using Water or Blizzard spells in combos will prevent them from setting themselves ablaze, meaning Sora can finish them without issue. They can also be used to put them out while charging around the area. Crystal Snow's Formchanges, the Blizzard Claws and Blizzard Blades, exclusively deal Blizzard damage and can keep them doused as well.