Matter-energy conversion was an incredibly powerful and dangerous application of magic in which the magician converts a portion of the matter making up their body, or presumably the matter making up any other object, into pure energy, which erupts outward in a cataclysmic explosion. The only confirmed users of this ability were Thuviel, who sacrificed himself in this manner in a final attempt to defeat the Forsworn on Vroengard, and Galbatorix, who at the end of the Rider War used this power to commit suicide in a final act of defiance after his defeat, causing grave damage to Urû'baen in the process, and completely destroying his citadel.