Question about mithralmist shirt....

[ASBERON88]

My halfling rogue/fighter/whisper knife has acquired a mithralmist shirt, and he's been doing some pretty devastating damage with it, however I don't think I've been doing this right, and wanted to check with you guys. The mithralmist shirt (pg. 20 MIC) says that Up to seven times per day, you can activate this +1 mithral shirt to fill your space with
a billowing silver mist. This gleaming fog grants you concealment against attacks but does not interfere with your vision. The mist lasts for 1 minute per activation, and it remains in the space where you activated the effect (it doesn’t move with you if you leave that space).

Now my question is, since he has concealment does he always get sneak attack damage with his ranged daggers (given that he's within 30 ft of course) as long as he remains in the mist or will he still have to do the standard hide check, throw weapon, and then hide with a -20 penalty like if he took cover behind a wall or something like that? If not then this cheap item is pretty game breaking if I'd say so myself.

[Biffoniacus_Furiou]

It does not give total concealment or invisibility, so it does not make it so his opponents are denied their Dex bonus to AC against his attacks. It gives concealment (20% chance to miss him), and it enables him to make hide checks as you described.

[Shnigda]

I think that I'd you activate the mist and then step 5ft behind it in such a way that the enemies could only see you through the mist, then you would get total concealment
E - - - - M P
E=enemy M=mist P=player -=5ft

Anyone else feel free to correct me if I'm wrong!

[Zaq]

It does not give total concealment or invisibility, so it does not make it so his opponents are denied their Dex bonus to AC against his attacks. It gives concealment (20% chance to miss him), and it enables him to make hide checks as you described.

Note that without HiPS, concealment alone isn't enough to Hide—you have to have concealment (or cover) and not be observed, which is pretty hard to make happen in the heat of battle.

[Surpriser]

I think that I'd you activate the mist and then step 5ft behind it in such a way that the enemies could only see you through the mist, then you would get total concealment
E - - - - M P
E=enemy M=mist P=player -=5ft

Anyone else feel free to correct me if I'm wrong!

The mist only provides concealment, so apparently it is not thick enough to completely block vision.
Whether you stay within the cloud or move behind it, all you get is concealment, which is (as was said before) not enough to make your enemies lose their Dex to AC.

[Shnigda]

However, if you step behind the mist and cast the mist again you definitely get total concealment as the mist acts like the spell "Obscuring Mist". Therefore if you are more than 5ft into the mist away from your target, you hace total concealment against them.
(Note, you may only gave normal concealment again other enemies who are looking at you from another angle and not through both squares if mist
E - - - M MP
MP=mist with player in it)

[Khedrac]

However, if you step behind the mist and cast the mist again you definitely get total concealment as the mist acts like the spell "Obscuring Mist". Therefore if you are more than 5ft into the mist away from your target, you hace total concealment against them.
(Note, you may only gave normal concealment again other enemies who are looking at you from another angle and not through both squares if mist
E - - - M MP
MP=mist with player in it)
But because the mist only fills a 5' square there is only 5' of mist between you and the observer = normal concealment.

[Shnigda]

Obscuring mist says that the enemy cannot see more than 5ft through the mist and anything beyond 5ft grants total concealment, so because you are behind a square of mist (and therefore more than 5ft through the mist), surely you would get total concealment as the enemy cannot see through the mist in front of you? (At least that is my interpretation of it... and fortunately my DM's)

[StreamOfTheSky]

Obscuring mist says that the enemy cannot see more than 5ft through the mist and anything beyond 5ft grants total concealment, so because you are behind a square of mist (and therefore more than 5ft through the mist), surely you would get total concealment as the enemy cannot see through the mist in front of you? (At least that is my interpretation of it... and fortunately my DM's)

Obscuring Mist also assumes there's more mist in the square behind that first 5 ft, since it's a 20 ft radius, while as the shirt is just a 5 ft square of mist. So I disagree with your interpretation.

In any case, the magic items gives you 7/day concealment as a swift action for only like 1000 gp, it's already possibly under-priced w/o trying to cheese it.

[Khedrac]

Obscuring mist says that the enemy cannot see more than 5ft through the mist and anything beyond 5ft grants total concealment, so because you are behind a square of mist (and therefore more than 5ft through the mist), surely you would get total concealment as the enemy cannot see through the mist in front of you? (At least that is my interpretation of it... and fortunately my DM's)

I have bolded the two key terms, and the second is incorrect.
Concealing Mist gives total concealment if you try to see more than 5' through it.
As single 5' square is not "more than" 5' - it is exactly 5'.
(OK, one can start worrying about diagonals, but here the D&D movement and distance rules kick in and the first square is only 5' regardless of angle.)

Yes you are trying to see more than 5', but not "more than 5' through the mist" - it's 5' through the mist and other distance through clear air.

Now if you drop the mithralmist just outside an area of obscuring mist then 5' step back into the mist you would have total concealment while your target would not.

[Shnigda]

But as the diagram above shows:
E - - - M MP
when you drop mist in one square, take a 5ft step backwards and drop another mist, then to see you the creature would be looking through more than 5ft of mist (unless you take up 25sqft of space). Even being 1 nanometre back into the second square of mist means that the enemy is looking through more than 5ft of mist (not much more, but still more) and therefore you get total concealment...
Or do you need 3 squares of mist and be in the rearmost one to get total concealment?
ie. E - - - M M MP

[Hiro Quester]

If you did this two squares of mist thing, it would be reasonable for your DM to rule that you also have trouble seeing the enemy, because you are also looking through more than five feet of mist.

At least as DM I'd say this tactic should give your enemy concealment against you.

[Surpriser]

I would let you get total concealment with only two uses of the shirt (with you standing in or behind the second square), but only against enemies directly ahead. Against enemies off to the side, you still only get concealment.
This is consistent with the way obscuring mist works.

Note that you need at least two rounds to pull that off (unless you have a way to get extra swift actions) and a single casting does not even enable you to make a hide check (unless you have HiPS) and definitely won't deny your enemies their Dex bonus to AC against your attacks.
Also, the (total) concealment you get does not mean that enemies do not know which square you are in. After all, it's the one square filled with mist that contains a dark shape in the middle.

EDIT:

If you did this two squares of mist thing, it would be reasonable for your DM to rule that you also have trouble seeing the enemy, because you are also looking through more than five feet of mist.

At least as DM I'd say this tactic should give your enemy concealment against you.
The mist created by the shirt explicitely does not interfere with your vision. But in general, yes, you are hampered by mist, smoke and dust in exactly the same way as your enemies (for example when casting obscuring mist).