An invisible creature is visually undetectable. Invisibility makes a creature undetectable by senses which require line of sight, including Darkvision, but most non-visual senses completely negate the benefits of invisibility. While they can't be seen, invisible creatures can be heard, smelled, or felt.
Against creatures which rely on visual senses, invisibility provides the following benefits:
- While invisible, if you are also using stealth, you can only be revealed by a creature that makes an active Spot check against you. Passive Perception checks may not be used against a stealthed creature which is also invisible.
- Your Stealth checks while invisible are made with a +2 circumstance bonus (+4 if you are standing still).
- Attacks made while invisible, against enemies who can't see you, are made with a +2 circumstance bonus to the attack roll, and the target is treated as flat-footed versus the attack.
- While invisible, you are not subject to precision damage (e.g. sneak attacks) unless the attacker has a targeting sense which pierces your invisibility and provides no miss chance.
Finding Invisible Creatures
If a creature has reason to be making active perception checks (Spot checks) against a stealthed, invisible creature (such as an alert guard), then the perception roll, within 30 feet, is resolved as normal against the creature's stealth result (with a bonus for being invisible).
A creature can seek to actively notice the presence of a non-stealthed, invisible creature within 30 feet, by making an Average DC Perception check (based on the invisible creature's CR (challenge rating) or level). A creature must make a Spot check to actively look for an invisible creature (which usually requires a move action to perform) — they will never perceive them with Passive Perception. There is normally no reason to look for invisible things, unless some other clue of their existence suggests that you look for them.
- A successful perception check reveals the square in which the invisible creature is located, but the creature still benefits from total concealment (automatically miss on a natural result of a 12 or less on the d20, and you must be attacking the square your target actually occupies).
- There are a number of modifiers that can be applied to this DC if the invisible creature is moving or engaged in a noisy activity.
A creature can also grope about to find an invisible creature using its sense of touch. A character can make a touch attack with his hands or a weapon into two adjacent 5-foot squares using a standard action. If an invisible target is in the designated area, the touch attack may land as long as the Natural Result on the attack die is 12 or higher, assuming the final number hits the target's Armor Class. If successful, the groping character deals no damage but has successfully pinpointed the invisible creature's current location. If the invisible creature moves, its location, obviously, is once again unknown.
If an invisible creature strikes a character, the character struck knows the location of the creature that struck him (until, of course, the invisible creature moves).
If a character tries to attack an invisible creature whose location he has pinpointed, he attacks normally, but the invisible creature still benefits from total concealment (automatically miss on a natural result of a 12 or less on the d20, and you must be attacking the square your target actually occupies). A particularly large and slow invisible creature might get a smaller miss chance at the GM's discretion.
If a character tries to attack an invisible creature whose location he has not pinpointed, have the player choose the space where the character will direct the attack. Whether or not the invisible creature is present in that square, conduct the attack normally. If the roll is below the Natural result needed, the player is informed they missed due to a poor roll. If the square is empty, and the player rolls well (above a natural 12, regardless of hit or miss), inform the player the square is empty. if the square is occupied, and the roll is above a 12 but still misses the creatures AC, inform the player the creature is present, but they do no damage. If the roll is sufficient to hit the monster, then it is resolved as a normal attack, and the player knows where the creature is.
Limitations of Invisibility
If an invisible character picks up a visible object, the object remains visible. An invisible creature can pick up a small visible item and hide it on his person (tucked in a pocket or behind a cloak) and render it effectively invisible. One could coat an invisible object with flour to at least keep track of its position (until the flour falls off or blows away).
Invisible creatures leave tracks. They can be tracked normally. Footprints in sand, mud, or other soft surfaces can give enemies clues to an invisible creature's location, assuming they can make the appropriate skill checks.
An invisible creature in the water displaces water, revealing its location. The invisible creature, however, is still hard to see and benefits from total concealment (automatically miss on a natural result of a 12 or less on the d20, and you must be attacking the square your target actually occupies).
An invisible burning torch still gives off light, as does an invisible object with a light or similar spell cast upon it. An invisible creature carrying an exposed source of bright light may still make a stealth check to mask both himself and the exact location of the light source. The light source is diffuse and difficult to pinpoint, but a pretty potent clue as to the creature's whereabouts. That is, a light source, even an invisible one, is passively noticeable by anyone with sight-based senses, and is automatically noticed. Most creatures will then wonder where the light is coming from, and make an active check to look for its source, triggering the opposed Perception vs. Stealth roll. If the invisible creature hasn't made a Stealth check, the opposed Perception check is against an Average DC (based on the invisible creature's CR (challenge rating) or level).
Invisible creatures cannot use gaze attacks.
Invisibility does not thwart divination spells.
Invisibility with Ethereal and Incorporeal
Ethereal creatures are invisible. Since ethereal creatures are not materially present, such creatures gain the bonus to Stealth checks even against some extraordinary senses, such as Tremorsense, since they are no longer interacting with the material plane like a normal invisible creature would. GM's are the final arbiter of which senses can ignore invisibility caused by being ethereal.
An even more extreme version of invisibility, faded creatures are difficult to remember in addition to being invisible.
Creatures wishing to attack a faded target must make a will save (DC 10 + creature's level or CR) to even remember that the target exists. If they succeed on the saving throw, they must still attempt to target the creature through its invisibility: determining its location, and dealing with the total concealment miss chance. If they fail the save, the faded creature is treated as out of range for that creature's attacks this round, even though they might otherwise be able to attack. They've forgotten about the faded creature entirely (for this round), and won't even try to attack them or include them in an area of effect.
Assuming that enemy creatures can continue to bypass or somehow target through the faded creature's invisibility (e.g. they have Tremorsense, etc.), the enemy creatures may make a new saving throw each round to attempt to pierce the Faded status as well.
When a save is failed, Faded also suppresses invisibility-bypassing effects and senses such as Glitterdust (Sorcerer/Wizard Spell), a barbarian's doodlebug, Blindsense, and other effects which allow targeting of invisible creatures (but only with regard to the Faded creature). If these effects are ongoing (as with Glitterdust (Sorcerer/Wizard Spell), Tremorsense, etc.), the creature can be targeted only on those rounds in which a successful save against the Faded status was made.