The wizard in my game had ablative barrier and resinous skin cast on him.
Ablative barrier converts the first 5 damage from each attack into non-lethal damage. Resinous skin grants DR5/piercing.
He got smacked by a bludgeoning attack.
How is the damage reduction and damage conversion resolved? Assuming the damage conversion resolves first, does the damage reduction reduce the lethal damage, non-lethal damage, or does the character get to choose?
Good question. I don't know if there is RAW to cover it, so I'd go by the old 3.5 standby of "whatever is best for the defender".
I think the affected person gets to choose which effect goes first.
But I can make your question even trickier:
What happens when an invulnerable rager with DR4/- which gets doubled vs nonlethal who happens to have ablative barrier on himself gets hit by an attack that deals damage?
Now the DR could either prevent 4 lethal or 5 (the ammount converted) nonlethal.
Could the barbarian choose to have the ablative barrier come first, converting the damage and then choose to have the nonlethal damage prevented (using up 3 DR) and 1 point of lethal damage?
As the first 5 points of lethal damage the character would take is converted to non-lethal, an Invulnerable Rager's DR of 4/- would apply first then the 5 damage he would normally take is instead converted into non-lethal, fortunately the Invulnerable Barbarian has resistance to non-lethal equal to double his DR. So effectively subtract 9 damage per attack and takes 5 damage away from the Ablative Barrier's max of 50 hp. An excellent addition to any Invulnerable Rager's defenses.
Ablative barrier converts the first 5 damage the target takes. Since DR reduces the amount of damage you would take, the DR is applied first.