Crystal Mask is a Seren spell requiring 90 Magic. Like the other Seren spells and prayers, this spell is a reward of the Light Within quest. It gives +15% to pickpocketing chance for five minutes, and gives a chance to not be stunned by NPCs who stun on catching a pickpocketing attempt. It can be re-cast at any point to refresh the duration.
Pickpocketing Dwarf traders with Crystal Mask and Light Form is around 700,000-810,000 experience per hour. This requires Ardougne cloak 3, Trahaearn exoskeleton set, any of the Five-finger discount aura, and/or level boosting items, e.g. God banner or the Abyssal lurker/Magpie familiars and their scroll specials which increases the amount of experience per hour. Cheeky monkey is also an option to prevent stuns, once a minute.
When used in conjunction with Light Form, the spell significantly reduces the rate of failing when checking urns at Pyramid Plunder.
Players who own the Black ibis outfit (bonus automatically factored in the exoskeleton set), legendary five-finger discount aura, the Recruit a Friend bonus, and clan avatar will have rates approaching 1,000,000 experience per hour.