Halon elemental

[J-H]

I'm thinking of this as a triggerable monster in a library.

If someone uses a Fire spell, a bell rings in the distance. One round later, a thick mist appears and surrounds the area where the fire was used; multiple Halon elementals will be deployed if needed.

The elemental appears as a large cloud filling a 20x20x20 cube.
Halon Elemental
Huge elemental (20x20)
CR around 3-5
HP around 80
AC 10
Good saves: CON
Stats STR 14, DEX 8, CON 20, INT 2 WIS 6 CHA 6
Immunities: Poison, non-magical weapons, fire damage
Resistances: Cold, psychic damage
Vulnerability: Thunder damage
Multiattack: Up to 6 misty tentacles per turn, 10' range. No more than two tentacles per target per round; the elemental will attempt to spread its attacks equally between any living beings within range, regardless of what faction they are associated with.
Slam +5 to hit, 1d6+2 damage; target must succeed on an opposed strength check or be knocked back 10' if hit.

No oxygen:
Fire spells do only 1/2 damage within the area of the Halon elemental
Anyone within the Halon elemental's misty body must make a CON save or be Slowed (as the spell) as they cannot breathe.
Persistent fire effects of 5th level and lower are neutralized within the area of the Halon elemental.
Fire-type enemies have Disadvantage whenever inside the area of the Halon elemental, and take double damage from its attacks.

The Halon elemental will attack in an attempt to keep anyone from being within 10' of it. It will not chase anyone who attacks it, but it will chase after any sources of fire within its blindsight range of 60'. It will discorporate after 3 rounds of no fire, regardless of whether or not it is being attacked.

[jjordan]

I like it. That's cool and fun.

[J-H]

This is totally exploitable by the players too. "I light a torch and throw it at the enemy spellcaster."

hacking and coughing ensues

[Chronos]

I like it, but you're missing the part about it actually putting out fires. And what would happen if you had a halon elemental and a fire elemental fighting?

Aside: Back in the day when I was playing a fire sorceress in Diablo II, I used "halon" and "asbestos" as obscenities.

[J-H]

Ok, I'll add something about that.

[Keravath]

I'd suggest 120' blindsight range or at least 120' detect fire range. I'd also suggest that the librarians are equipped with amulets so that the elementals won't attack them if triggered unless the librarian is holding an open flame. You wouldn't want the fire suppressant system killing off your librarians when a forgetful wizard tips over their candle.

Anyone engulfed should start to suffocate, though since there are still gases present it should still be possible to cast spells with verbal components.

Also, if these are to be deployed as defensive systems then anyone that has been observed using fire should remain a target until they have left the library. For example, characters casting firebolt, lighting or carrying a torch or other open flame or casting (gasp) fireball should remain priority targets of the elementals until they are subdued or have left. Anyone without association with flames would only be a target within 10' of the elemental. You could bump up its wisdom a bit to account for these behaviours. Perhaps make its INT 3 or 4 to account for their training.

[MrStabby]

Maybe some acid resistance would be appropriate as well?

[J-H]

What's the idea behind acid resistance? I'm not sure I see where it's coming from.

[Chronos]

Persistent fire effects of 5th level and lower are neutralized within the area of the Halon elemental.
And what if the ranger just piles up a bunch of logs and kindling and so on, and lights it with a nonmagical flint and steel? You want to add non-magical fires to that, too.

[J-H]

Yep. I'm DMing the game so I'm the only one who will even look at the exact ruleset for this one unless someone asks for it later.

[MrStabby]

What's the idea behind acid resistance? I'm not sure I see where it's coming from.

Just that most halon compounds are much less reactive to acid than say, your average adventurer. Not immune, but more resistant.

[Arkhios]

A minor nitpick, but saying "20 feet cube" is not only accurate but also much more simple than "20X20X20 cube". The dimensions are already implied in the word "cube" ;)

[jjordan]

To expand upon my comment: I think your halon elemental should only attack fire. Any attacks on individuals should be incidental and only related to the attacks on fire (if the character is close to the fire when the elemental attacks, is in a space the elemental needs to occupy to attack a fire, etc....) It shouldn't be more substantial than a cloud of gas.

Or, at least, that's how mine will be when I steal implement this idea in my setting

[Phhase]

I feel like a large area full of an unbreathable gas would begin to suffocate anyone inside...

Cool idea though, Redcloak would be proud.