Subtle Spells
Source
The Threefold Conspiracy: The Chimera Mystery pg. 51
You can disguise your spellcasting to confound onlookers. If you succeed at a Sleight of Hand check (DC = 10 + 5 × level of spell being cast) while casting a spell (this requires no extra action), choose a different spell of the same level and school as the one you are casting. An onlooker who succeeds at a Mysticism check to identify the spell you are casting believes the disguised spell to be the other spell you chose unless their result exceeds the DC by 10 or more. A spell with an obvious effect (such as explosive blast) will immediately disabuse of the onlooker of their false assumption. You can’t actually eliminate all signs of spellcasting, so security footage may still reveal you as the source of dangerous magic.
Starting at 5th level, you can spend 1 Resolve Point to automatically succeed on the Sleight of Hand check. When you do so, the onlooker takes a –2 penalty to a Mysticism check to identify your spell and the DC to counter your spell with dispel magic or greater dispel magic increases by 2.
ID
724390a0c76628987c42eb1d