If I understand it correctly, you get concealment (other than from powers) from lighting conditions or being in certain squares.
[sblock=Concealment]OBSCURED SQUARES
- Lightly Obscured: Squares of dim light, foliage, fog, smoke, heavy falling snow, or rain are lightly obscured.
- Heavily Obscured: Squares of heavy fog, heavy smoke, or heavy foliage are heavily obscured.
- Totally Obscured: Squares of darkness are totally obscured.
Effects that cause concealment obscure vision without
preventing attacks.
CONCEALMENT
- Concealment (–2 Penalty to Attack Rolls): The target is in a lightly obscured square or in a heavily obscured square but adjacent to you.
- Total Concealment (–5 Penalty to Attack Rolls): You can’t see the target. The target is invisible, in a totally obscured square, or in a heavily obscured square and not adjacent to you.
- Melee Attacks and Ranged Attacks Only: Attack penalties from concealment apply only to the targets of melee or ranged attacks.
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If you make a stealth check then I guess the creature can't see you
[sblock=Targeting what you can't see]If you’re fighting a creature you can’t see—when a creature is invisible, you’re blinded, or you’re fighting in darkness you can’t see through—you have to target a square rather than the creature.
You also have to figure out which square to attack. Here’s how it works.
- Invisible Creature Uses Stealth: At the end of a concealed creature’s turn, it makes a Stealth check opposed by your passive Perception check. If you beat it, you know there’s a creature present that you can’t see, and you know the direction to its location. If you beat it by 10 or more, you know exactly what square the creature ended its turn in. The concealed creature also makes a Stealth check if it
takes an immediate action or an opportunity action.
- Make a Perception Check: On your turn, you can make an active Perception check as a minor action, comparing the result to the concealed creature’s last Stealth check. If you win, you know the direction to the creature’s location, or its exact location if you beat it by 10 or more.
- Pick a Square and Attack: Choose a square to attack, using whatever information you’ve gleaned so far about the target’s location. Roll the attack normally (taking the –5 penalty for attacking a creature that has total concealment). If you pick the wrong square, your attack automatically misses, but only the DM knows whether you guessed the wrong square or your attack just missed.
Close or Area Attacks: You can make a close attack or an area attack that includes the square you think (or know) the concealed creature is in. Your attack roll doesn’t take a penalty from the target’s concealment.
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So the system would seem to be
Tyron's turn, get concealment, make stealth check (one roll) vs. each Kobold (actively rolled). If you succeed you've "disappeared". They don't know where you are, though they do know where you were when you were last not concealed.
--At this point you get combat advantage against them.
At the -end- of Tyron's turn you make stealth check vs their passive perception. If you make -that- check they can't see you till your next turn (and then only if you attack or bring attention to yourself). If you miss by up to 9 then they know you're there and the direction but not which square (Still have combat advantage).
-If you miss by 10 then they see you.
They can take minor actions during their turn to search for you. If they win by 10 they can see you, otherwise they just know you're "there" and which direction.
If they ever have LOS, or you otherwise lose concealment then you have to do it all over again. But if Tyron doesn't attack, keeps moving three or more squares a round and makes the stealth checks each round vs their passives (and their minors if they start searching)? Then he's still "effectively invisible".