Autocast is an option of many Magic weapons, primarily staves, that can be activated on the combat section of the interface. This attack option causes players to automatically cast a selected spell when they attack, as opposed to manually selecting the spell and its target each time you wish to cast it. Once autocast has been selected, a player will continue casting spells as their default attack as long as they wield the staff and have the correct amount of runes.
The spells that can be autocasted vary between magic weapons. No teleportation, alchemy, curses, or enchantment spells can be autocasted.
The Void Knight mace can autocast the Claws of Guthix spell, making it the only mace with the autocast ability, and making Claws of Guthix one of the two God spells with the autocast ability (along with the Staff of the Dead with Flames of Zamorak).