PCs aren’t the only characters who can roll a critical success—their adversaries can too! Whenever you roll a 20 on the d20, your roll automatically succeeds.

If you critically succeed on an attack roll, you also deal extra damage. Start with the highest possible value the damage dice can roll, and then make a damage roll as usual, adding it to that value. For example, if the damage dice are 2d8+2 and you critically succeed on the roll, you would automatically deal 16 damage. You then roll the dice and get a 5 and a 7. So you add 16+5+7 for 28, plus 2 for the modifier, for a total of 30 damage.

A critical success on a reaction roll does not have any added benefit for an adversary.