Perfect juju agility potion

A Perfect juju agility potion is a potion made using the Herblore skill. Drinking a dose of this potion provides one of two effects upon completing a lap at the Prifddinas Agility Course:
 * The window shortcut to the cathedral roof is open.
 * There is a light creature on top of the cathedral roof.

To make a 3-dose potion, combine a scentless potion with one harmony moss. Making the potion requires 85 Herblore and provides 101.3 xp.

Reference

 * http://services.runescape.com/m=rswiki/en/Perfect_juju_agility_potion