Practical aspects of fire immunity

Question

Fire immunity certainly defends the creature against magic attacks with fire description. But I'm curious about natural hazards.

How does a fire immune creature react to a extremely high temperature? Suppose we find a way to put the creature into high-temperature plasma. Rules preserves that creature from any harm dealt by fire (and high temperatures as rightful assumption).

But what will become with the creature in details? Does it gains extremely high temperature but preserves its form? Will it radiate corresponding to gain temperature? Or may be fire immune creature just keep its preferred temperature and fire immunity prevents temperature transition? Then there would be area of relatively low temperature where evaporated tungsten would condense and so suffocate the creature. Its a very spectacular way to finish a foe. But is it still legal with regards to rules?

Answer 1

D&D is not a physics engine

Some rules, because they seem to simulate little bits of reality, might give you the impression that this is major point of the game. However, D&D reality is very skewed in favour of making games and fantastical stories. Neither games, nor fantasy novels nor cinema pay much more than lip service to science-based reality. This extends to pretty much all role-playing games - some try harder than others, but all ultimately fail, and require either DM rulings (of course subject to DM's understanding of reality) or accepting "it's just a game".

The D&D world breaks many laws of physics

Many game effects appear to break core conservation laws, such as conservation of energy - although you can posit magical energy of various kinds, I doubt you could really fix that. A lot of the science-based effects (e.g. Time Stop) are based on fantasy science that really doesn't work if you think too hard about it (and I'm not talking about impossibility of the spell - think for a moment what is happening to the atoms and photons in a Time Stop zone - how could you see anything in it?)

Fire immunity is an example of introducing an "immovable object", and your plasma idea is the "unstoppable force". This was an old philosophy conundrum when the two met, but modern physics would consider either concept as a nonsense.

The situation is unlikely to come up unless you construct it

Perhaps there is a magical trap that the players could find out about that generates a metal plasma, and it can be used to effectively petrify Fire Immune creatures caught in it. It might be a fun scenario to play. The chances of it happening without the players and the DM actively making it happen are unlikely though.

More mundane "reality" questions pop up now and then, when rules either don't exist, or seem to clash with real-world sense. You can rule these how you like, but I would advise to err on keeping the game and story alive as a priority over your sense of "reality".

Rule weird or unusual situations how you think they should work

A plasma of super-heated metal is a little out-of-canon for D&D, although if you find it fun, why not go for it. There is no RAW

On a simpler variant, I would rule a Fire Immune creature could drown in lava, much the same as a more normal creature would drown in water. There may even be RAW for this, although I haven't checked.

Double-check a few things afterward

If you enjoy exploring unusual situations in the game, you may want to check:

• Other people in your group also find them fun

• That you have not created an easy win option that would change the game and make it boring (all Fire Immune monsters can be defeated with the new tungsten plasma wand)

Answer 2

Mechanically, creatures that have fire immunity are only immune to fire.

Fire immunity doesn't, by RAW, automatically allow a creature to easily traverse a desert without endurance, or heal when subjected to a fire-based attack (that would normally be a seperate ability).

In terms of "super-heated plasma," the closest thing to this that a fire-immune creature would encounter (within the system) would probably be a high-level spell. Perhaps electricity or other forms of energy. Again, this creature is only immune to fire and would therefore be effected normally by the spell.

Creating scenarios that are outside of the system is probably a bad idea for a GM unless they have already discussed this sort of thing with the players. In all honesty, real-world physics have no place at the table. RAW act as their own sort of "physics" within the game's system and are there for a reason: They make the game playable. In this case immunity to fire has a strict meaning within the rules of the system.

There may be cases where the rules are ambiguous, but I wouldn't consider energy immunities one of them. Creating a scenario where the players have to wonder if you've set up your fire elemental to be immune to that pillar of plasma in the middle of the room (that looks nothing like fire) would be bad form on the part of the GM, especially if the players manage to force the elemental into the pillar only to have the GM say "Surprise! You've only made it stronger!" (Unless its a skill challenge and the players had access to that information during/before the encounter, but I digress as that's for another question/answer.)