Stealth
Stealth gives you a chance to avoid the notice of one or more enemies. Activating Stealth can be done as part of another action that would not normally attract attention. If, at the end of your stealthy action, you don't have cover or concealment against a given enemy, your attempts at stealth have no effect against that enemy and it notices you.
Stealth is sustained against an enemy until that enemy notices you. If at any time you lose cover or concealment against an enemy or act in a way likely to attract notice (run, attack, speak etc..) it will notice you immediately following that action.
Perception: If an enemy's stealth check does not exceed your passive perception you notice the enemy. If you are aware of or suspect an enemy's presence you can try to make an active perception check to notice the enemy once per round as a free action. If that check exceeds the stealth check, then you notice the enemy.
Aid another's Perception: If you notice an enemy acting stealthily you can, as a free action, try to inform an ally of the enemy's presence and location. This gives a +2 bonus to an active perception check to notice the enemy. If you use a minor action to try and help your ally perceive the enemy, it equates to a +6 bonus to the ally's perception check to notice the enemy.
Combat Advantage: If stealth is successful against a given enemy, it grants combat advantage against that enemy.
Modifiers to Stealth check: These modifiers apply to stealthy actions but also apply to the stealth check even after it has been made. So if a person with a stealth check of 20 chooses to walk 4 squares their stealth check is reduced to 15 during the round in which they moved. Of course, if their movement takes them out of cover or concealment they will be noticed anyway.
Move more than 2 squares as a single move action. -5
Ran. -10
For each size category you are above medium. -3
Modifiers to Perception Checks:
For each ally who can see the stealthed enemy and communicates their location to you as a free action: +2
For each ally who can see the stealthed enemy and communicates their location to you as a minor action: +6
Stealthy person was in plain site of you (no cover or concealment) during some part of the turn in which they made the stealth check: +4
For every 10 squares between you and stealthy enemy: -4
Begin or end your turn adjacent to an stealthy enemy with normal cover or concealment: +8
Begin or end your turn adjacent to an stealthy enemy with total concealment or superior cover: +4
Effects of no line of sight, blindness, darkness, invisibility etc..: If the enemy has no line of sight to you or otherwise can't see you (i.e. they are blinded, you are invisible etc..) the enemy's perception check (or passive perception) must be at least 10 higher than your stealth check in order to pinpoint your location. If the perception check exceeds your stealth check by less than 10, they are aware of your presence, general direction and general distance only. Because the Perception check will be based solely on senses other than sight, the DM is encouraged to include additional penalties based on the presence of ambient noise and similar circumstances that would make the perception of a completely unseen enemy more difficult. Suggested penalties for ambient noise against stealth checks of unseen enemies: Loud (battle, waterfall, thundering stampede, etc..) -10. Moderate (conversation(s), presence of others nearby who aren't stealthy, river, banjo playing, etc..) -5.
Effects of being unnoticed and unsuspected: If, because of successful use of stealth, you are unnoticed by an enemy and the enemy doesn't suspect your presence, that enemy can't target you directly with an attack and acts under the assumption that you don't exist.
Effects of being unnoticed but suspected: It is possible that the enemy doesn't notice you or can't see you directly but still suspects your presence, This can happen either because they were aware of your presence before you used stealth or because their perception check exceeded your stealth by less than 10 but they have no line of site to you. In this case, the enemy can make a guess as to your location and act accordingly. This may include moving in an attempt to become adjacent to you or to gain a line of site past the cover or concealment. They can also attempt an attack on the square(s) they think you may occupy. If they get lucky and attack the square in which you actually are hiding their attack is subject to the penalty for total concealment.
Stealthy Actions: Stealthy actions are ones during which you can choose to make a stealth check or which you can perform while sustaining stealth. A stealthy action has to be one which normally wouldn't attract attention. Therefore, attacking stealthily, shouting, running or playing the banjo stealthily are not possible. Walking is a good example of a move action that can be done stealthily. Simply ducking is a good example of a minor action that can be done stealthily. Unless provided for by a power, free actions or interrupt actions can't be used to make a stealth check.
Common sense exceptions and situations
Attacking from the same place: You can't use stealth to gain combat advantage against an enemy you've already attacked from the same square. For example, if you are firing from behind an arrow slit, you can't choose to fire, then duck stealthily to fire again with combat advantage from the same arrow slit against the same enemy next round. The enemy has to have some reason to believe you are no longer in that square (this could be achieved through a successful bluff for instance).
Attacking in the same round as stealthing: You can't gain combat advantage from stealth in the same turn in which you made the stealth check unless the enemy does not suspect your presence. (i.e. you can't do some stealthy move or minor action to gain combat advantage for an attack made that same turn unless the enemy doesn't suspect your presence).
Movement and stealth: As noted, unless an enemy has reason to believe you are no longer in a given square, they aren't likely to be fooled by stealth. So, if an enemy has noticed you (perhaps because you fired on him or are playing the banjo), and you then use stealth as a minor action, the enemy will probably guess you are still in that square even if they don't succeed on a perception check. So, the farther you move, the harder it is for the enemy to guess which square you are in. Remember that if you move more than 2 squares in a single move action, you take a -5 penalty to your stealth check that round.
