Castigation

When you make a melee weapon attack, you can take a -7 penalty to the attack roll. If the attack hits, the target is castigated until the end of your next turn.

While castigated, whenever the target deals damage, it takes 1d6 radiant damage for each instance of damage it deals. A dragon that uses its breath weapon on three party members takes 3d6 radiant damage. A creature that makes two claw attacks and both hit takes 2d6 radiant damage.