Frostbite and DR

Question

Frostbite

Your melee touch attack deals 1d6 points of nonlethal cold damage + 1 point per level, and the target is fatigued. The fatigued condition ends when the target recovers from the nonlethal damage. This spell cannot make a creature exhausted even if it is already fatigued. You can use this melee touch attack up to one time per level.

First of all, my Dm has choose to consider the Frostbite ( delivered through spellstrike ) like a riding magical effect.

From book ...

Spells, spell-like abilities, and energy attacks (even non-magical fire) ignore damage reduction.

So how Frostbite interact with ...

1. monster with dr 10/-
2. monster immune to frost damage
3. Monster immune to non-lethal damage

Im not able to understand if having one "dr/immunity" is enought to block the damage, or if the damage is considered a "double type" and are needed both types of dr/reduction to prevent it ( For example a morningstar - B and P - can bypass a 10/piercing )

If a weapon causes two types of damage, the type it deals is not half one type and half another; all damage caused is of both types. Therefore, a creature would have to be immune to both types of damage to ignore any of the damage caused by such a weapon.

Bonus question :

Regardless of this, witht he above formula , if one use spellstrike with frostbite with a rapier(P) versus a monster with ( DR 5/slashing | 5 cold resistance ) both part of the damage get eventually reduced, right?

Answer 1

1) Monster with dr 10/

It takes full damage, as Damage Reduction only reduces physical damage from natural attacks or weapons (falling, suffocation, starvation, etc, ignore DR aswell).

Frostbite is energy damage. The difference here is that this damage is recovered faster than lethal frost damage.

Energy Damage

Energy damage is typically dealt by spells (usually evocation spells such as fireball or cone of cold) and typically deals hit point (hp) damage, but unlike damage dealt by weapons or natural attacks, damage reduction usually is not effective against it. Instead, a creature typically must have energy resistance to reduce the amount of damage it takes from one of these sources.

Spells or effects with any of the descriptors [acid], [cold], [electricity], [fire], or [sonic] typically deal energy damage. Energy resistance is usually effective against these types of energy damage.

2) monster immune to frost damage

It takes no damage because the damage is frost AND nonlethal.

3) Monster immune to non-lethal damage

It takes no damage because the damage is frost AND nonlethal.

Regardless of this, witht he above formula , if one use spellstrike with frostbite with a rapier(P) versus a monster with ( DR 5/slashing | 5 cold resistance ) both part of the damage get eventually reduced, right?

Correct, it will reduce 5 damage from the rapier, and another 5 from frostbite.

Spells that Deal Physical Damage

Certain spells will say it deals bludgeoning, piercing or slashing, but be warned, these spells will ignore Damage Reduction aswell, unless the Damage Reduction is specifically against those damage types.

Example, a zombie has DR 5/Slashing. It will reduce 5 damage from an Ice Storm, that causes 2d6 bludgeoning damage, plus 3d6 cold damage (which will ignore DR).

Source

Answer 2

DR never affects energy damage, just plain ol' weapon damage. While you are delivering them in one "package", so to speak, treat them as separate and completely normally within the rules to determine the effect of defenses thereon. The part you quote about B/P weapons is only talking about weapon types, it is not relevant in this case.

So for a melee attack doing nonlethal cold, the melee part is reduced by DR, the cold part is reduced by cold resistance, and any nonlethal damage is ignored by a creature that ignores nonlethal damage.

You may want to look at the other questions under the pathfinder and damage-resistance tags. Specifically, note that you will still deal the energy damage even if all the weapon damage is negated due to DR.