Fiend, Stage 2 (Brand of the Chainer's Gaze)

As a bonus action on your turn, you can brand a creature within 60 feet of you with a fiery mark that diminishes their resolve. The target must make a Wisdom saving throw, and on a failed save they are branded. Whenever a creature branded in this way makes a saving throw, they must roll 1d6 and subtract the result from their saving throw. A creature remains branded this way for 1 minute. The brand disappears if the creature is knocked unconscious, enters hallowed ground, or is targeted by the remove curse spell. You may use this feature a number of times equal to your Charisma modifier (minimum of 1). You regain all uses of this feature when you finish a long rest.

Flaw

Aversion to Radiant.

If you take radiant damage, you have disadvantage on attack rolls and ability checks until the end of your next turn.