Void runes are a form of noncraftable rune. They can be obtained as a drop from Dragonite dragons, Rune dragons, the Barrows dragon, the Crystal dragon or as a reward for beating the Grim Reaper in a fight when you're in The Void, with only 5% against the Reaper and 2% against the dragon, which is why they cost so much. They are only used in Loste Magicks, in the spells Annihilate and Steal Life. The new spell book, Noob Magicks, also needs a void rune in it's most powerful spells.