(How) does obscuring mist affect the caster inside it?

Question

One of my players' characters can use his armor to cast obscuring mist in the square where he is.

I'm pretty sure what happens to the enemy that wants to attack him while he stays in the fog, but I'm not sure what happens to him.

He is a rogue that uses a bow to fight: while he is inside his fog, can he target enemies with his bow without any penalties?

What happens if he moves away, and an ally goes inside the fog?

EDIT: Thanks for you answers. I have checked the name and yes is the Mithralmist armor. I don't have the manuals right now, I must investigate more on it and understan if Obscuring Mist is a prerequirements or not

EDIT2: Ok as someone of you says, with the Mithralmist armor the fog doesn't effect the vision of who wear it. So the rogue not only can see without any problem, but have concealment (20% melee, 50% ranged) and can do sneak attack.

Answer 1

The description of mithralmist shirt is somewhat vague. It not necessarily creates a fog similar to that of Obscuring Mist spell (item's prerequisite to be created), but 'billowing silver mist' it creates still lacks some info to be clear enough as a separate standalone effect.

As written it neither doesn't interfere with your attacks when you shoot from the space filled with it, nor doesn't interfere with your attacks when you leave that space. Also, as written, it grants concealment only to you (sireously, that may be the reason why it doesn't interfere with your vision with no caveats). Those assumptions are questionable while possible. In this case your rogue may shoot freely. But what happens to ranged attacks of those entering his bank of mist is mostly left on DM's mercy.

Another way to interpreate given item is to assume it creates a bank of fog similar to that of it's prerequisite spell. That bank just happens to be only as large as your space is and is in that space when you activate the shirt. That way whole discriptive text stays largely true, but we know what to do with cases not touched by it.

If we go this way, either rogue or anyone entering the fog may fire their bows with no hindrances. Obscuring Mist confers concealment depending on the distance between¹ creatures in squares containing the fog. You may treat that as if armor owner was standing on the border of regular Obscuring Mist's effect. As your rogue (or any creature for that matter) stands right next to the border² of a clouded area there actually are no squares of fog between her and her target. So her target gains no concealment.

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1. ^{For a creature to see into a square that creature's line of sight must be traced into that squere. So a target's squere also counts as part of a distance.}

2. ^{If your rogue is larger than medium, things may got more complicated. As there will be more than one square to enter, entering creature may position itself in a way it isn't adjacent to the border with respect to it's target. Not to mention, if armor owner himself moves, he may do the same.}

Answer 2

Unless a spell says otherwise, they affect everyone in their area. That includes the rogue as well as any of the rogue’s allies. The Complete Adventurer ninja has a variant in an issue of Dragon magazine that even boasts as its primary class feature an ability to use obscuring mist without affecting the ninja himself. This replaces the ninja’s usual invisibility, to give you an idea of how potent that is. It is definitely not an automatic part of the spell.

As such, obscuring mist is generally seen as an emergency escape option, a way to prevent attacks against you and allow you to flee. It can be awkwardly used for surprise melee attacks, but the miss chance is pretty high so that isn’t recommended.

The rogue could also blind-fire his bow through the mist. If he picks the right square, he has a 50% chance of missing outright (before he even gets to compare his attack roll against the target’s AC), but since the target has concealment from him, he cannot use precision damage—like sneak attack—on that target.

Answer 3

I'm actually loosely familiar with the armor you are talking about (if it's homebrew, there is an actual RAW version, just so you know). I don't recall the name off the top of my head (that said, I'll probably find it in the next few days anyway).

Anyhow, to the point of the matter -- if this is the armor I think it is (and I only know one that does this), then RAW I believe it does state he is immune to his own armor's ability.

Allies, however, are not covered in that statement.

Please note that I'll probably be nagged by this question, so this answer will likely be edited once I find the reference.

EDIT: Yep. Found the armor -- it's called Mithralmist Armor. Tenative citation is MIC, but I'll have to dig further to check this.