When you or an ally within 30 feet of yourself that can see or hear you makes a D20 Test, you can take a Reaction to give that creature Advantage on the roll.
You can use this feature a number of times equal to your Charisma modifier (minimum of once), and regain all expended uses when you finish a Long Rest. If the creature still fails the D20 Test, this use of Merrymaker isn't expended.