The trait states, in part, "you halve any reductions in visibility from the environment (such as from certain storms) and their corresponding penalties. For example, if you were in a sandstorm that normally reduces visibility to 25 feet and imparts a –4 penalty on Perception checks, you reduce visibility to 50 feet and take only a –2 penalty on Perception checks."
The key word seems to be environment. Is a magic spell such as Fog Cloud considered the environment? It definitely makes an environmental effect, but by RAW I don't know for sure. One could easily say the environment is a clear plain, and tossing a temporary magical mist in doesn't count.
Assuming the trait does work in a Fog Cloud, it would then allow a medium creature wielding a reach weapon to see and attack a creature 10 feet away, with a 10% miss chance from a halved concealment? Related to that, would it deny the attacked creature it's dexterity bonus since it can't see the attacker? Would it deny the attacked creature's dex even if the attacker couldn't see either?
If the answer is no, that it wouldn't affect Fog Cloud, does that extend to all magical environment effects? Cloudkill? Control Weather? How about a Cauchemar Nightmare's smoke ability, a supernatural effect?
For a bonus! Darkness is an environmental effect, and makes many creatures blind as a result. Would those be halved? Penalties for blindness include... "A blinded creature loses its Dexterity modifier to AC (if positive) and takes a –2 penalty to AC.
A blinded creature takes a –4 penalty on Perception checks and most Strength– and Dexterity-based skill checks, including any with an armor check penalty. A creature blinded by darkness automatically fails any skill check relying on vision."
I think it should work for weather-like spell effects, but expect table variation.
In a fog cloud you would see 10 ft but would have a 20% miss chance. The miss chance does not come from the spell but from the partial/total concealment status effect that the spell applies.
I believe that since your foe can't see you, you would also get +2 to hit and he would lose his dexterity bonus. However by RAW, this bonus only applies if you have the invisible condition or if your opponent has the blind condition.
(And as an aside, I think that by RAW if you are invisible and your opponent is blind he would have -2 ac and you would get +2 to hit. So there is that)
Agreed about it working for weather-like effects. Just doing the usual checking if there is a rules somewhere that I missed, but seems very likely it's just GM discretion.
Good catches on the concealment, lack of blindness, & lack of invisibility! By RAW none of those would be affected. Though again I imagine many if not most GMs would give something. As the attacker would be effectively invisible.
Unsure how I'd rule myself on darkness, spells like Cloudkill, or the supernatural smoke ability. Probably a no on darkness, since it'd halve weird things like the dex penalty and that's just a pain. Yes on the Cloudkill just cause it's so similar to fog. Yes on the supernatural smoke. But curious about other thoughts, course! It could make a couple of random spell concealment builds much more plausible.
I can see not everyone agreeing on this one.
For me magical effects that are created are not the environment, but magic that alters the environment would be fine.
(that's a no to fog cloud but a yes to control weather).
I wouldn't allow it to affect darkness, but that is more from my interpretation of the RAI than the RAW. I'm not 100% sure how I'd effectively argue the position.