Concealment
Originating from sources such as dense smoke and battlefield position, concealment obscures precise senses and imposes a miss chance on attacks. When you have concealment, it’s harder for enemies to see you clearly. This might be due to your position on the battlefield, or it might be due to another effect that makes it more difficult for enemies to perceive and hit you with an attack.
To determine whether you have concealment from a creature’s ranged attack, choose a corner of the enemy’s square. If any line from this corner to any corner of your square passes through a square that provides concealment or the border of such a square, you have concealment. Also use these rules when a creature makes a melee attack against a target that isn’t adjacent to it.
When a creature is making a melee attack against an adjacent target, the target has concealment if its space is entirely within an effect that grants concealment.
Additionally, some effects provide concealment against all attacks, regardless of whether any intervening concealment exists.
Source
Core Rulebook pg. 253
Concealment gives the target of a successful attack a chance that the attacker actually missed. This is called a miss chance. Normally, the miss chance for concealment is 20%. Make the attack normally; if the attacking creature would hit, the target must roll a 20 or lower on a d% roll (see page 513) to avoid being struck. Multiple concealment conditions do not stack. Source Core Rulebook pg. 253 |
Certain situations can provide more or less of a miss chance than typical concealment. In this case, it is up to the GM to determine a character’s degree of concealment. Source Core Rulebook pg. 253 |
If a creature has line of effect to you but not line of sight (see page 271), you have total concealment. An enemy can’t attack you when you have total concealment, though it can attack into a square it thinks you occupy. A successful attack into a square occupied by an enemy with total concealment has a 50% miss chance (instead of 20%). Source Core Rulebook pg. 253 |
Concealment might be ineffective. Dim light or darkness doesn’t provide concealment against creatures with darkvision. Creatures with low-light vision can see in dim light as if it were normal light. Source Core Rulebook pg. 253 |
