Crumble Undead is spell that requires a magic level of 39 to cast and costs 2 air runes, 2 earth runes and 1 chaos rune. It has a max hit of 15. This spell can only be cast on undead enemies, such as skeletons, zombies, ghost and shades. Crumble Undead is a good way to train magic, as it costs less runes than Earth Bolt (same if you are wielding a staff of earth) and hits as hard as Earth Blast. On the downside, it can't be auto-cast without a slayer staff. It is highly recommended against Slash Bash - The boss of Zogre Flesh Eaters quest.
- Trying to attack a non-undead NPC with Crumble Undead says " This spell only affects skeletons, zombies, ghosts and shades".