For context, my character just got pounded by flaming boulders. She is currently immune to fire for story reasons, so the fire damage is null. However, she has to make a dexterity saving throw against the bludgeoning damage. It deals 60 damage, however if she succeeds she takes half damage.
What happens if she rolls a natural 20?
I know the damage is halved because she did succeed, but are there any other reductions to damage because of her natural 20 roll?
(Note: For our house rules we play with the premise that a natural 20 is an automatic success and a natural 1 is an automatic fail)