Hexcrest

The Hexcrest is a unique Slayer item dropped by Jungle Strykewyrms. In order to equip it, a player must have a Magic level of 20, a Defence level of 10, and a combat level of 40. It boosts the player's Magic strength by 15% against their slayer task monsters. It can be combined with a Focus sight and a Slayer helmet to form a Full slayer helmet. With the Staff of light, a 7 level boost from an extreme magic potion or overload potion, and a Hexcrest or Full slayer helmet worn against an assigned slayer monster, the theoretical (if all of those things stack, which is unsure of at the moment) damage percentage boost would be 51%, potentially adding half of the total damage of already powerful spells like Fire Surge or Ice Barrage