Mystic Will is a Prayer that gives 2 bonus levels to a player's Magic skill when calculating hit chance. It cannot be used in conjunction with any of the other prayers that provide a magic, ranged, attack, or strength bonus. It is the first prayer to which players have access that affects magic and the fifth prayer to which players have access. All of the Halos reduce the drain rate of this prayer to 2/3 of the normal rate (0.33 times lower).
The update history project is a work-in-progress – not all updates to this topic may be covered below. See here for how to help out!