Shield (3.5e Creature Ability)
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Shield is a protection unique to certain creatures, most of which are constructs. A shield defends the creature it envelopes and has the ability to soak damage of most any kind. A creature with the shield special quality has a deflection bonus to Armor Class equal to half its HD (with a minimum of +1 and a maximum of +10). For every HD a creature has, the shield that protects it has 5 hit points. Shield hit points are regained at a rate of 1 hit point per HD per hour. When a shield's hit points are depleted, its deflection bonus to AC disappears until the shield gains at least 1 hit point, unless otherwise noted in the creature listing.
Shield Absorption: As long as a shield has hit points remaining, it can absorb damage of virtually any kind, from physical damage types (bludgeoning, piercing, slashing) to energy damage types (acid, cold, electricity and fire), to force damage, to even most typeless forms of damage. Shields are even effective to touch attacks. Shield absorption functions as both a damage reduction/- and damage resistance of 10 plus 5 for every 5 HD, to a maximum of 30. Damage dealt over this amount bypasses the shield and is dealt to the creature itself. A shield cannot absorb more damage than it has hit points at any time. After the damage of an attack is reduced by shield absorption, any remaining damage is still susceptible to any other damage reduction or resistance to energy types the creature may have.
Only certain damage dealing effects can pass through a shield, such as a sonic effect, a gaze attack or psionic effects. Spells that do not deal damage and that do not require touch are unaffected by a shield.
Certain powerful war machines have more powerful shielding. The greater shield special quality does not have a shield absorption limit, but absorbs all damage from any attack until it depletes, and furthermore never loses its deflection bonus. A greater shield regains a number of hit points per round equal to 10 plus an additional 5 points for every 5 HD the creature has (similar to fast healing).
Certain machines possess shielding that does not only protect themselves, but also creatures or other machines that surround them closely. Perimeter shields are always of the greater variant, possessing a number of hit points and a recharge rate that corresponds to the HD of the creature possessing the shield, but instead of just granting its deflection bonus to just the creature that projects it, it grants that bonus to ranged attacks against all the creatures that reside within the field. When an attack breaches a perimeter shield, the damage that remains after being reduced by the shield is lost. Unlike ordinary shields, perimeter shields cannot be passed physically at all in either direction until the shields are down. All physical attacks are affected by the shield, including the ones that are made from inside it against creatures outside it. The machine possessing the perimeter shield mey either choose or be programmed to still allow energy-based ranged weapons, effects or spells to pass through the shield to target those outside it normally.
Perimeter shields are always projected as a spherical field with a radius of 10 ft. or twice the reach of the creature that possesses it, whichever is higher. The shield is not adversely affected by movement; when the shield is forced to inhabit a space that contains a wall or floor due to the creature controlling it moving around, it simply passes through those things.