Crumble Undead is a unique combat spell found in the standard spellbook. Requiring only 39 Magic, it's capable of hitting 16 against undead enemies such as zombies, skeletons, ghosts, shades, and so on. It can only be used against undead creatures, but offers a max hit equal to that of much higher level blast spells. In order to autocast Crumble Undead, you must equip a Slayer Staff, Staff of the dead, Staff of light, or a Void knight mace.

Many players choose to use this spell in the battle against Vorkath, as the spell is able to instantly kill the Zombified Spawns which are summoned during the fight.

A Magic level of 39 is required to use this spell, giving 24.5 experience. It requires 1 Chaos rune, 2 Earth runes, and 2 Air runes to cast.