Identify spells, read magical signs, understand occult lore, or sense what something unnatural is doing.
There are people who see the glyph on the door and step over the threshold anyway. This is one kind of courage, and it kills a lot of them. There are people who see the glyph and read what it is asking for, and decide whether to give it. Knowledge of magic is not power over it — but ignorance of magic is not safety from it either, and the two are often confused.
Mysticism is the skill of understanding the supernatural — identifying spells, reading magical signs, knowing what an occult glyph demands, sensing what a cursed object is doing, and navigating the occult traditions of the world without stepping on the wrong thing. Make a Mysticism (Intellect) Trial when dealing with phenomena that have a magical or supernatural basis. For broader lore and dead traditions, see Knowledge (Intellect); for living cultural and spiritual practice, see Tradition (Spirit).
Examples: identifying what a warding glyph is triggered by; reading the residue of a spell to understand what was cast; recognizing the binding conditions on a summoned creature; knowing enough of a cult’s ritual logic to disrupt it.