Leomund's Tiny Hut - Poison Gas

This is really going to be down to you, the DM, and what you want the players to experience.

It could be argued that at the very least you would need to dispel the gas within the area to ensure it isn't in the Hut when it the hut is formed. There's nothing in the spell description that states it would purify already toxic air, so I think that's a fine assumption. So the party using a spell slot to cast Gust or using some ability to clear the air before the Hut casting finishes could make sense. But the question might be: why are you making them do that? Are you trying to get them to run low on spell slots or use resources? If not, and you're just going to let them get a long rest anyway, then you're really just slowing down part of the session for no real impact. Now if the players come up with this idea independently, then maybe it's a fun thing to play off of. But You as the DM saying "first you need to spend a spell slot before you can long rest, when you'll get the spell slot back anyway" just adds a random burden with no real narrative benefit. But if you're playing a more gritty/"realistic" campaign, maybe that's something you want anyway.

Otherwise, if you want your party to suffer exhaustion or give them a time crunch to "open the doors to area 39", then just say the gas goes through the Hut and they can't get the benefit of a Long Rest due to taking damage every hour. This will press the party to find a way out of the area with the gas and give them a sense of urgency. If THAT is what you want, make the gas go through the Hut barrier. 

It doesn't seem like there is a RAW answer either way, so decide what is going to be A) fun for the party and B) effective for the narrative, pacing, and overall feeling of the session/dungeon.

Quote from MaximusArael020 >>

This is really going to be down to you, the DM, and what you want the players to experience.

It could be argued that at the very least you would need to dispel the gas within the area to ensure it isn't in the Hut when it the hut is formed. There's nothing in the spell description that states it would purify already toxic air, so I think that's a fine assumption. So the party using a spell slot to cast Gust or using some ability to clear the air before the Hut casting finishes could make sense. But the question might be: why are you making them do that? Are you trying to get them to run low on spell slots or use resources? If not, and you're just going to let them get a long rest anyway, then you're really just slowing down part of the session for no real impact. Now if the players come up with this idea independently, then maybe it's a fun thing to play off of. But You as the DM saying "first you need to spend a spell slot before you can long rest, when you'll get the spell slot back anyway" just adds a random burden with no real narrative benefit. But if you're playing a more gritty/"realistic" campaign, maybe that's something you want anyway.

Otherwise, if you want your party to suffer exhaustion or give them a time crunch to "open the doors to area 39", then just say the gas goes through the Hut and they can't get the benefit of a Long Rest due to taking damage every hour. This will press the party to find a way out of the area with the gas and give them a sense of urgency. If THAT is what you want, make the gas go through the Hut barrier. 

It doesn't seem like there is a RAW answer either way, so decide what is going to be A) fun for the party and B) effective for the narrative, pacing, and overall feeling of the session/dungeon.

 

I don't think blowing air around works, because the air that will replace the air you blew will also have poison gas.  It might be possible to clear a volume of air somehow, but it's going to require way more cleverness than 'i cast a spell, done'.  (And this is an 'I'm going to need at least 5 minutes to think about this' problem, it's not obvious.)

Narratively the gas should have a couple of effects:

• They try to LTH -> LR, they figure out in an hour or two that the poison gas is stopping them from taking a long rest (and are 1-2 d6 hp down.)  Depending on how low on resources they are, and how far into the dungeon they are, they might face the prospect of a harrowing trip back up to where the air is safe, with monsters having had a couple hours to move around and do things.  (Or even find this weird impenetrable thing and decide to watch it.)
• It limits how quickly the lower dungeon can be explored.  They need to burn resources healing while exploring the area, they need to plan for a trip back to where the air is good, and there'll be no short rests at all while they're in it.  And when they can't explore the whole thing in one adventuring day, they'll have to go back the next day - and monsters may have moved, reset traps, etc... and so they'll have to burn resources re-exploring areas they've already explored.  Yes, the dungeon changes when they're not there.  The rooms don't move, but what's in them might.

I'd actually recommend cribbing B/X dungeon procedures.  Out of combat actions happen in dungeon turns = 10 min.  In that time, you can carefully explore (and map) 120' of dungeon, or investigate a 10'x10' area, or pick a lock quietly, or etc...  Check for wandering monsters every two turns.   A torch lasts 6 turns. A combat takes a full turn.  (Sure, the fighting might be over in 4 rounds, but then you take a breather, bandage wounds, clean weapons, check gear, etc...).  Doing things faster creates noise, which triggers more wandering monster checks.

5e does have some dungeon procedure, but it's not emphasized (and pretty scattered), and it's not dangerous enough.  Wandering monster checks are too infrequent, and actions are too fast (1 min for many things; you generally explore areas too quickly).  And that lack of standardized time makes time-keeping harder (because everything isn't measured in the same standard 10min block).  

Quote from MaximusArael020 >>

then you're really just slowing down part of the session for no real impact.

I would say establishing the vibe of the dungeon -- that even the air will kill you eventually if you don't do something about it -- is not "no real impact"

Within the context of the adventure, the purpose of the gas is to add time pressure and make it impossible to complete a long rest. As such, it fails to do its job if tiny hut works against it.

Quote from AntonSirius >>

Quote from MaximusArael020 >>

then you're really just slowing down part of the session for no real impact.

 

I would say establishing the vibe of the dungeon -- that even the air will kill you eventually if you don't do something about it -- is not "no real impact"

 That's why I said this part: "It doesn't seem like there is a RAW answer either way, so decide what is going to be A) fun for the party and B) effective for the narrative, pacing, and overall feeling of the session/dungeon.

For reference, Hidden Shrine of Tamoachan was originally a tournament module with a primary goal of 'make it out alive'.