"At a Magic attack bonus of -65, Stun will never hit the target; this is achievable by equipping metal armour and a set of vambraces. However, if the player isn't satisfied with -69, it can at least be lowered to -75 if he player wants to, by wearing a fighter hat, 3rd age warrior platelegs and a 3rd age vambraces." http://runescape.wikia.com/wiki/Stun You need to get -65 magic attack bonus.