My doubt is when I have to calculate the damages on the Invidiak: I have to apply first is incorporeal quality and then his DR or I have to apply first his DR and then the incorporeity?
Sorry if my english may be incorrect
Incorporeal first - then DR. Taking Ice Storm as an example as it's called out in the DR section we'll go through it.
Shadow Demon has the following:
Defensive Abilities incorporeal; DR 10/cold iron or good; Immune cold, electricity, poison; Resist acid 10, fire 10; SR 17
Ice Storm has the following descriptor:
Saving Throw none; Spell Resistance yes
Great magical hailstones pound down upon casting this spell, dealing 3d6 points of bludgeoning damage and 2d6 points of cold damage to every creature in the area. This damage only occurs once, when the spell is cast. For the remaining duration of the spell, heavy snow and sleet rains down in the area. Creatures inside this area take a –4 penalty on Perception skill checks and the entire area is treated as difficult terrain. At the end of the duration, the snow and hail disappear, leaving no aftereffects (other than the damage dealt).
Incorporeal says this:
Incorporeal (Ex) An incorporeal creature has no physical body. It can be harmed only by other incorporeal creatures, magic weapons or creatures that strike as magic weapons, and spells, spell-like abilities, or supernatural abilities. It is immune to all nonmagical attack forms. Even when hit by spells or magic weapons, it takes only half damage from a corporeal source[b]. Although it is not a magical attack, holy water affects incorporeal undead. [b]Corporeal spells and effects that do not cause damage only have a 50% chance of affecting an incorporeal creature (except for channel energy). Force spells and effects, such as from a magic missile, affect an incorporeal creature normally.
An incorporeal creature has no natural armor bonus but has a deflection bonus equal to its Charisma bonus (minimum +1, even if the creature's Charisma score does not normally provide a bonus).
An incorporeal creature can enter or pass through solid objects, but must remain adjacent to the object's exterior, and so cannot pass entirely through an object whose space is larger than its own. It can sense the presence of creatures or objects within a square adjacent to its current location, but enemies have total concealment (50% miss chance) from an incorporeal creature that is inside an object. In order to see beyond the object it is in and attack normally, the incorporeal creature must emerge. An incorporeal creature inside an object has total cover, but when it attacks a creature outside the object it only has cover, so a creature outside with a readied action could strike at it as it attacks. An incorporeal creature cannot pass through a force effect.
An incorporeal creature's attacks pass through (ignore) natural armor, armor, and shields, although deflection bonuses and force effects (such as mage armor) work normally against it. Incorporeal creatures pass through and operate in water as easily as they do in air. Incorporeal creatures cannot fall or take falling damage. Incorporeal creatures cannot make trip or grapple attacks, nor can they be tripped or grappled. In fact, they cannot take any physical action that would move or manipulate an opponent or its equipment, nor are they subject to such actions. Incorporeal creatures have no weight and do not set off traps that are triggered by weight.
An incorporeal creature moves silently and cannot be heard with Perception checks if it doesn't wish to be. It has no Strength score, so its Dexterity modifier applies to its melee attacks, ranged attacks, and CMB. Nonvisual senses, such as scent and blindsight, are either ineffective or only partly effective with regard to incorporeal creatures. Incorporeal creatures have an innate sense of direction and can move at full speed even when they cannot see.
Damage Reduction says this:
Damage Reduction (Ex or Su) A creature with this special quality ignores damage from most weapons and natural attacks. Wounds heal immediately, or the weapon bounces off harmlessly (in either case, the opponent knows the attack was ineffective). The creature takes normal damage from energy attacks (even nonmagical ones), spells, spell-like abilities, and supernatural abilities. A certain kind of weapon can sometimes damage the creature normally, as noted below.
The entry indicates the amount of damage ignored (usually 5 to 15 points) and the type of weapon that negates the ability.
Some monsters are vulnerable to piercing, bludgeoning, or slashing damage. Others are vulnerable to certain materials, such as adamantine, alchemical silver, or cold-forged iron. Attacks from weapons that are not of the correct type or made of the correct material have their damage reduced, although a high enhancement bonus can overcome some forms of damage reduction.
Some monsters are vulnerable to magic weapons. Any weapon with at least a +1 magical enhancement bonus on attack and damage rolls overcomes the damage reduction of these monsters. Such creatures' natural weapons (but not their attacks with weapons) are treated as magic weapons for the purpose of overcoming damage reduction.
A few very powerful monsters are vulnerable only to epic weapons—that is, magic weapons with at least a +6 enhancement bonus. Such creatures' natural weapons are also treated as epic weapons for the purpose of overcoming damage reduction.
Some monsters are vulnerable to good-, evil-, chaotic-, or lawful-aligned weapons, such as from an align weapon spell or the holy magical weapon property. A creature with an alignment subtype (chaotic, evil, good, or lawful) can overcome this type of damage reduction with its natural weapons and weapons it wields as if the weapons or natural weapons had an alignment (or alignments) that matched the subtype(s) of the creature.
When a damage reduction entry has a dash (—) after the slash, no weapon negates the damage reduction.
A few creatures are harmed by more than one kind of weapon, such as “cold iron or magic.” A weapon that inflicts damage of either of these types overcomes this damage reduction.
A few other creatures require combinations of different types of attacks to overcome their damage reduction (such as “magic and silver”), and a weapon must be both types to overcome this type of damage reduction. A weapon that is only one type is still subject to damage reduction.
Format: DR 5/silver; Location: Defensive Abilities.
FAQ on DR says this:
How does DR interact with magical effects that deal bludgeoning, piercing, or slashing damage?
Although the Bestiary definition of Damage Reduction (page 299) says "The creature takes normal damage from energy attacks (even nonmagical ones), spells, spell-like abilities, and supernatural abilities," that's actually just referring to damage that isn't specifically called out as being of a particular type, such as fire damage or piercing damage. In other words, DR doesn't protect against "typeless damage" from magical attacks.
However, if a magical attack specifically mentions that it deals bludgeoning, piercing, or slashing damage, DR affects that damage normally, as if it were from a physical weapon. (Otherwise the magical attack might as well not have a damage type, as it would only interface with B/P/S damage in a very few corner cases, such as whether or not an ooze splits from that attack.)
For example, the ice storm spell deals 3d6 points of bludgeoning damage and 2d6 points of cold damage. If you cast ice storm at a group of zombies, the zombie's DR 5/slashing protects them against 5 points of the spell's bludgeoning damage. Their DR doesn't help them against the spell's cold damage because DR doesn't apply to energy attacks.
So from all that lets (for the example) pretend this is a maximized ice storm - 18 points of bludgeoning and 12 points of cold.
First - the spell needs to make a resistance check - assuming that succeeds we move on.
Next we go to anything the creature is immune to - in this case cold - so it ignores the 12 points of cold - we do this only because if it's immune it doesn't matter if anything else modifies this damage - so it doesn't pay to waste any more time thinking about it.
Now we move onto the bludgeoning - in this case we find the line in incorporeal that states it will only take half damage from a spell (other than force) that does damage - so 9 bludgeoning. This is because it's not reducing the damage by 50% - that 50% 'passes through' the creature or misses - much like a more powerful form of invisibility or cover.
Finally we apply DR to the damage that *did* effect it DR 10/cold iron or good. Well based on the FAQ we know the damage from Ice Storm is typed and that *does* matter - in this case it is bludgeoning but it is not cold iron or good - so we take 10 away leaving 0 (never negative) letting a shadow demon ignore a maximized ice storm as if it didn't exist.
Hope this helps.
Thanks everyone!