Jacobious Justinious III's Prestige 1 Feat
Your prolonged connection to Maqaroth has led you towards understanding how to use his wrath to your advantage. Whenever you take fire damage or deal fire damage to a creature, you gain a stack of Wrath. The maximum amount of Wrath you can have at one time is 4. If an enemy scores a critical hit on an attack against you, you instantly gain maximum Wrath. Wrath can be used in the following ways:

• When you hit a creature with a melee weapon attack you can deal additional fire damage to the target equal to 3 per Wrath spent.
• When you make a Constitution saving throw to maintain concentration on a spell you can increase the result of your roll by 1 per Wrath spent.