Staff of light

"The Staff of light is a unique drop from Ice Strykewyrms. You need 75 attack and magic to wield this weapon. It can be used as a Slayer's staff, it has stats roughly equivalent to a Dragon weapon, it causes +15% Magic damage, it has a special attack that reduces any melee damage that is received by 50% for one minute, and has a 1/8 chance of not using up runes each time a damage-dealing spell is cast with it.

The rune-saving effect can be combined with a full set of Combat robes (improving the chance to 1/5) or Battle robes (for a 50% chance of saving runes). Each of these robe sets can both be earned as rewards from the Fist of Guthix minigame. Also, any time the staff does not save the player runes, the robes themselves will still have their usual chance of saving the player any mind, chaos, death or blood runes used by the combat spell the player is casting."

Combat and magic styles
The staff of light gives the best magic attack bonus for any one handed staff besides the master wand.

Activating the special attack will cause all melee attacks to do just half the normal damage for one minute. If you un-equip the staff while the special is activated, you will lose the effect.