Having no physical body. Incorporeal creatures are present on the same plane as the characters, and characters have some chance to affect them. Incorporeal creatures are immune to all nonmagical attack forms. They are not burned by normal fires, affected by natural cold, or harmed by mundane acids. They can be harmed only by other incorporeal creatures, +1 or better magic weapons, spells, spell-like effects, or supernatural effects. Even when struck by spells, magical effects, or magic weapons, however, they have a 50% chance to ignore any damage from a corporeal source -- except for a force effect, such as magic missile, or damage dealt by a ghost touch weapon. Incorporeal creatures are immune to critical hits, extra damage from being favored enemies, and from sneak attacks.
An incorporeal creature has no armor or natural armor bonus (or loses any armor or natural armor bonus it may have when corporeal), but it gains a deflection bonus equal to its Charisma modifier or +1, whichever is greater. Such creatures can move in any direction and even pass through solid objects at will, but not through force effects. Therefore, their attacks negate the bonuses provided by natural armor, armor, and shields, but deflection bonuses and force effects (such as mage armor) work normally against them, as does anything with the ghost touch ability.
Incorporeal creatures have no weight and do not set off traps that are triggered by weight. They do not leave footprints, have no scent, and make no noise, so they cannot be heard with Listen checks unless they wish it. Incorporeal creatures cannot fall or take falling damage. Likewise, they cannot manipulate objects or exert physical force on objects. They move in any direction (including up or down) at will. They do not need to walk on the ground. Though they can pass through solid objects at will, they cannot see when their eyes are within solid matter.
Incorporeal creatures hiding inside solid objects get a +2 circumstance bonus on Listen checks, because solid objects carry sound well. Pinpointing an opponent from inside a solid object uses the same rules as pinpointing invisible opponents. Incorporeal creatures pass through and operate in water as easily as they do in air.
Corporeal creatures cannot trip or grapple incorporeal creatures.