Source: Tal'Dorei Campaign Setting Reborn

The challenges and struggles you've faced throughout your life have led you to delight in inflicting pain and anguish upon others. You gain a number of cruelty dice equal to your proficiency bonus. Your cruelty dice are d6s. You can roll only one cruelty die per turn, and a cruelty die is spent when you roll it.

You can roll a cruelty die under any of the following circumstances, with the indicated result:

• When you deal damage to a creature, spend one cruelty die to deal extra damage to the creature equal to the roll.
• When you score a critical hit, spend one cruelty die to gain temporary hit points equal to the roll.
• When you make a Charisma (Intimidation) check, spend one cruelty die and add the roll to your check.

You regain all spent cruelty dice when you finish a long rest.