Opacity is the difficulty of a Mystery to be solved, the ways that it resists and defies understand; it hides itself from the Sight of Mages. Opacity is assigned for each character individually, and is reduced separately by Scrutiny
Setting the Opacity rating for a given Mystery is in the Storyteller’s hands. It isn’t something that should have a hard-and-fast formula to it, because if the players figure out that having Opacity 4 always means a four-dot spell is in effect, it lessens the impact of solving the Mystery.
Guidelines for Opacity
These are some guidelines for the Storyteller, just a couple of general rules
The higher the Arcana, the higher the Opacity
A decent rule of thumb is for Opacity to be rated equal to the highest Arcanum used in a spell, as a base. This means that a mage should be able Scrutinize a one-dot spell in a single turn, but that’s appropriate; such spells aren’t terribly involved.
This leads nicely into…
Complexity increases Opacity
A spell that involves five different Arcana all at one dot would certainly have a supernal lore higher Opacity than a single-Arcanum spell. Increase Opacity by one per extra Arcanum used.
Remember the Math
An Opacity 4 Mystery doesn’t take four successes to unravel. It takes 10 (four to drop it to Opacity 3, three more to drop it to Opacity 2, and so on). An Opacity 6 Mystery requires 21 successes to fully unravel. Think very carefully before assigning Opacity ratings higher than 5.
Mages can cloak their Magic
Hiding a Mystery from Scrutiny is part and parcel to the Awakened. They layer “decoy” spells on top of Mysteries, use Prime to send would-be Scrutinizers down false paths, and set traps for careless investigators. You can represent these things with high Opacity, and set the “truth” at the deeper levels of the Mystery.
Non-Supernal Phenomena are more Opaque
A mage can Scrutinize the site of a Wasteland created by a Promethean and learn a great deal, but the Opacity rating should be higher (roughly 1.5 times higher, as a suggestion) than a similar effect created by Awakened magic.