You can take a Bonus Action to trace the Yellow Sign in the air and create a 10-foot Emanation of psychic energy centered on yourself for 1 minute or until you have the Incapacitated condition. Once per turn, when a creature within the Emanation makes a D20 Test, you can roll 1d6 and subtract it from the roll (no action required).
Once you use this feature, you can't use it again until you finish a Short or Long Rest unless you expend one Battle Die (no action required) to restore your use of it.