Things you can't see and things you can't find, in D&D.
Knowing what you can and can't see, and what you can and can't target, and knowing when you get to say "I aim at the invisible guy in that square" versus "I don't know where he is, I'll just guess", is very important in D&D. The purpose of this mini-guide is to clarify the rules for Stealth and invisibility, and how they interact.
The Premises, AKA The Core Rules That You Need To Know FIRST:
The First Premise: Everyone knows where everyone else is, at all times, period.
No, seriously. EVERYONE. EVERYWHERE. ALWAYS. There is no such thing as a combatant whose current position you do not know. Except....
The Second Premise: There is one and only one exception to The First Premise, and that exception is Hidden.
The status "Hidden", achievable only through rolling Stealth, is the only exception to this. It is the only way by which anyone can be uncertain about the current position of anyone else.
If you are not Hidden, EVERYONE KNOWS WHERE YOU ARE, PERIOD. If you are Hidden, anyone you are Hidden from must guess your current location.
This is going to be repeated a few more times in the text below, because it is the most important thing to remember and it heavily impacts everything else.
For the record, I capitalise "Hidden" as it is a specific game concept with a specific meaning, even though the book does not. The book really should - Hidden is a real state, a real condition, and it SHOULD be covered as a fully capitalised game term with a glossary entry, not simply be left to be defined in the Stealth Skill entry.
Now that that's covered, let's cover some basic concepts:
"Concealment": Partial LOS failure, usually provided by a class feature, terrain feature, or magic item. You are NOT invisible and you CAN be seen. Concealment is enough to MAINTAIN Hidden, but not enough to BECOME hidden.
"Total Concealment": You are invisible. Nobody can see you, but unless you're also Hidden, they still know where you are. You can *become* Hidden, but you are not inherently Hidden.
"Invisible": You have Total Concealment. No, seriously, that's all Invisibility means. Nothing less, NOTHING MORE. Invisibility is NOT Hidden.
"Hidden": The state of being able to conceal your location. If you are Hidden, enemies have to guess your square. If you are not Hidden, they know where you are, at all times.
To recap: IF YOU ARE NOT "HIDDEN", YOUR ENEMIES KNOW WHERE YOU ARE, PERIOD, whether they can see you or not. If something doesn't SAY you are Hidden, you are not Hidden, period.
How do you become Hidden? You roll Stealth at the end of any Move Action or any of your Actions (even Free Actions) during which you move.
"Move" is defined in the PHB3 glossary as, roughly, to leave one square for any reason to enter another square. You can't roll Stealth after Forced Movement since that's not your action. You CAN roll Stealth after a granted Free Action.
You must also meet three requirements:
1) You must not be visible, which means Total Concealment or Superior Cover, at the end of the move.
2) Your Stealth roll must beat the Passive Perception of anyone you want to be Hidden from
3) You cannot have HAD Hidden at the start of the action and lost it during the action. Which is to say, you can't BECOME Hidden as part of the same action that loses your Hidden state.
By the way, any time you become Hidden, record the number you rolled. It's important.
Q: Once you are Hidden, then what?
A: Anyone who wants to attack you must guess what square you are in. Note that you became Hidden AT THE END of a Move, and you weren't Hidden until after the end of the move. Everyone knew where you were before you became Hidden, which means they knew where you were AFTER you became Hidden. If you haven't moved out of that square, they technically have to guess your location but, really, they're going to guess "where you where when they lost you". If you don't move AFTER becoming Hidden, you're not going to avoid a lot of attacks.
Q: If I'm Hidden, I'm Hidden from EVERYONE, right?
A: No. Technically, Hidden only applies to enemies, so your allies ALWAYS know where you are unless you're specifically hiding from them, too. Also, Hidden only applies to people against whom you meet the requirements. If you only have Total Concealment from one enemy, you CAN become Hidden from that enemy, but you CAN'T become Hidden from his friends.
Q: So I'm Hidden, that means I'm safe now, right?
A: No. Now that you are Hidden, you are a member of a very prestigious and selective club: Hidden Club.
Hidden Club has rules that you must obey, or you will be kicked out.
The Rules Of Hidden Club: Losing Hidden
The First Rule Of Hidden Club:
Stay out of sight. If, at ANY TIME, you lack at least Cover or Concealment from an enemy, you lose Hidden against that enemy. It doesn't matter if this is your turn or his, or if it's in the middle of a move, or because a Wall got broken down. No Cover and No Concealment = EXPELLED FROM HIDDEN CLUB. Oh, and this means REAL cover - the kind of Cover you get against Ranged attacks by hiding behind an ally doesn't count.
The Second Rule Of Hidden Club:
Keep quiet. Anything louder than a whisper, or any environmental interaction above the same kind of level, expels you from Hidden Club.
The Third Rule Of Hidden Club:
Keep Still. If you don't move more than 2 squares at a time, you have no chance of losing Hidden. If you move more than 2, you have to roll Stealth with a penalty in order to stay a member of Hidden Club - and every time you do, your new number replaces your old number, for better or worse.
The Fourth Rule Of Hidden Club:
Don't Attack. If you attack, you are immediately Expelled From Hidden Club, period.
The Fifth Rule Of Hidden Club:
Don't let the enemy FIND you. An enemy can spend a Minor Action to roll Perception, and if he beats your Stealth (you DID write it down, right?), you lose Hidden. As well, any enemy who attempts to move into your space automatically finds you, period.
The Unspeakable Final Rule Of Hidden Club:
When you do something to lose Hidden, you keep the benefits of being Hidden until the end of that action. So moving out into the open costs you Hidden, but you keep Hidden until the end of the *entire action* - so if your action is Deft Strike, which lets you move *and* attack as part of the same action, you're Hidden during the attack part even though the Move part of it lost you Hidden. Similarly, if you have a power that lets you attack then move, attacking costs you Hidden but you *are* still Hidden during the move, until the full action is over.
Things you need to ask your DM about because the rules don't address them
Q: "if a monster is Hidden from Joe but not from me, can I tell Joe what square it's in?"
A: Yes, but the concept of "squares" is not an in-game thing for the most part, and some GMs think it should be difficult to tell your allies EXACTLY what square an enemy is in. Other simply say "you know where it is, talking is a Free Action, as long as you WANT to tell your allies where the guy is, you can."
Which GM is yours? I don't know. You need to ask him.
A: As of the Rules Compendium, there is now an explicit rule for this on page 150: Yes, you CAN point out the exact square of any creature you are aware of, to anyone else.
This does NOT mean that the creature is no longer Hidden, or that anyone else can perceive it - but as long as they believe you when you tell them what square it's in, they can "guess" the right square automatically.
So, as long as PCs are sharing information and can take Free Actions, anyone who breaks Hidden can tell everyone else what square to target.
Q: "if a power says I can roll Stealth to become Hidden, does that remove the normal requirements for Total Concealment/Superior Cover?"
A: This is unclear. As-written, both sides have arguments. However, the effects of the different rules are such that a bunch of inconsistent things and additional sources of confusion arise if the requirements to become Hidden are bypassed, while leaving the requirements to become Hidden intact makes those powers a little weaker but results in no confusion or inconsistency.
I personally am convinced that "does not remove the normal requirements because it does not specifically say it removes the normal requirements" is the proper reading, but that's me. Statistically speaking, you probably don't play in my game. So ask your GM.
As of the Martial Power 2 FAQ, this has been answered: You DO need to meet all the normal requirements to become Hidden, unless the power specifically says that it overrides the normal requirements.
The bit about you most likely not playing in my game is still true, statistically speaking.
Now, for some common questions.
Q: What about guys really far away, with a distraction, etc?
A: That's a situational penalty to the Perception skill, as per DMG.
Q: What about guys in the NEXT encounter? Do I know about them? Do they know about me?
A: No. They don't exist yet. The rules for Stealth and becoming Hidden apply only to creatures in the current Encounter.
Q: But I'm invisible! My enemies can't see me! They should have to guess where I am!
A: You may be invisible, but you're not inaudible, unsmellable, undetectable (think Predator), and you're not Hidden. Since you haven't put the work in to become Hidden, THEY KNOW WHERE YOU ARE.
Q: But I'm invisible AND they're Blind AND they're 30 squares away AND I'm downwind AND there's a giant roaring waterfall next to me! Shouldn't they have NO CLUE where I am?
A: Not if you're not Hidden. By the way, I'm counting something close to a +30 situational bonus there - take your NO ACTION and ROLL STEALTH at the end of your next move. Sheesh!
Q: Can I "move 0" and become Hidden?
A: Yes, if you used a Move Action. Same with standing up - any Move Action, or any action that lets you Move.
Q: Doesn't all this make Hidden REALLLLLY hard to get and maintain?
A: Kind of, yes - but that's intentional. Being Hidden isn't just about Combat Advantage, it's about virtual immunity to attack. As long as you're Hidden and can get away from your last known location unfollowed, you are almost completely immune to attacks and anything targeting you is almost certainly going to miss, outright, without a roll.
This is very, very powerful. And so it's hard to do. If you're just going Hidden to get Combat Advantage, it's actually a lot easier - but you don't get the immunity to attacks that way.
Anything not clear? Tell me, I'll add it to the post.