When you receive a physical attack and Shield Block it, if it deals multiple types of damage, how is damage reduced?

Question

Shield Block states that:

Trigger While you have your shield raised, you would take damage from a physical attack.

You snap your shield in place to ward off a blow. Your shield prevents you from taking an amount of damage up to the shield’s Hardness. You and the shield each take any remaining damage, possibly breaking or destroying the shield.

While a "Physical Attack" is not clearly defined in the rules, Physical Damage is:

Physical Damage

Damage dealt by weapons, many physical hazards, and a handful of spells is collectively called physical damage. The main types of physical damage are bludgeoning, piercing, and slashing. Bludgeoning damage comes from weapons and hazards that deal blunt-force trauma, like a hit from a club or being dashed against rocks. Piercing damage is dealt from stabs and punctures, whether from a dragon's fangs or the thrust of a spear. Slashing damage is delivered by a cut, be it the swing of the sword or the blow from a scythe blades trap.

There is a Core Rulebook Clarification (4th printing) regarding Shield Block:

Shield Block can only be used against physical damage from attacks, since non-attack effects can't trigger the Shield Block. For instance, if you walk over a square of hazardous terrain that deals piercing damage to you, having your shield raised doesn't help you, nor does it help if you need to make a Reflex save against a spell that deals bludgeoning damage. Some abilities let you use Shield Block with other triggers, as seen in the shield spell and the fighter's Reflexive Shield feat, but these exceptions are noted. Also note the 4th printing errata to spellguard shield (page 588) allows it to apply in this way.

If a Good-aligned creature with Shield Block used it with a Steel Shield (Hardness 5/HP 20) against a Cacodaemon's jaws attack that dealt 3 Piercing + 3 Evil damage, how would the damage resolve? And does that change for Mental, Poison, or Positive/Negative Damage?

Answer 1

Hardness Applies to *All Damage

An item can be broken or destroyed if it takes enough damage. Every item has a Hardness value. Each time an item takes damage, reduce any damage the item takes by its Hardness. The rest of the damage reduces the item’s Hit Points.

You could certainly use Shield Block against the cacodaemon's jaws as a physical attack with the piercing damage being dealt, and the rules for Hardness make no exception for the type of damage being dealt.

More reasonably, this means that you could block something like a red dragon's jaws to protect yourself from the physical and fire damage. This is explicitly called out in the description for the dragonslayer's shield:

The shield has resistance 10 against the damage type corresponding to the type of dragon whose hide was used in its creation; this applies after reducing the damage for Hardness.

However, alignment damage and positive/negative damage have their own exceptions:

Weapons and effects keyed to a particular alignment can deal chaotic, evil, good, or lawful damage. These damage types apply only to creatures that have the opposing alignment trait

Two special types of energy damage specifically target the living and the undead. Positive damage harms only undead creatures, withering undead bodies and disrupting incorporeal undead. Negative damage saps life, damaging only living creatures.

Unless your shield is a creature with the Good trait it can't be affected by the evil damage, so the shield's hardness wouldn't apply regardless of the normal rules for Hardness. It also wouldn't be affected by any positive or negative damage unless it's actually a creature and alive or undead.

Object Immunities

Inanimate objects and hazards are immune to bleed, death effects, disease, healing, mental effects, necromancy, nonlethal attacks, and poison, as well as the doomed, drained, fatigued, paralyzed, sickened, and unconscious conditions. An item that has a mind is not immune to mental effects.

If your shield has a mind then it could block mental damage for you, but otherwise items are similarly unaffected by mental and poison damage

Hardness Reduces Total Damage

Finally it's worth noting that Hardness lacks any special behavior for multiple instances of damage like in this case, so the item only reduces the total damage by its Hardness rather than reducing each damage type individually. For an adult red dragon dealing 20 piercing and 7 fire blocked with the same steel shield you'd take 22 damage rather than 17.

Answer 2

It actually should depend on the type of the "secondary" damage, and DM should apply logic where possible

When an attack applies different types of damage it depends on the nature of the attack, for example:

• When you have a flaming sword, it applies slashing and fire damage. You can block the blade blow, but fire and heat still can harm you even through your shield, although it could be somewhat reduced as the flames doesn't reach your skin.
• A serpent's bite could do piercing and poison damage. Here, if you completely block piercing damage, the bite really got stopped by your shield, so poison damage never kicks in, as the poisoned fangs get stopped without reaching your skin.
• A thunderous hammer would apply bludgeoning and lighting damage, your shield can stop the bludgeoning damage, but if you use a metal shield the damage from lighting could even get increased.

So, not every instance of "secondary" damage will apply the same way as every source it's different and can interact on a different way with your shield, or even with it's nature or material.

As with almost every situation that is not completely explained by rules, DM's discretion (and desirably a bit of logic) should apply.