7

The party will eventually be facing Tiamat, as an end-of-campaign event. At the present time, they are considering the effectiveness of wall of force as a defensive barrier against her.

Wall of Force is 5th level and says:

Nothing can physically pass through the wall.

Tiamat has:

Limited Magic Immunity. Unless she wishes to be affected, Tiamat is immune to spells of 6th level or lower. She has advantage on saving throws against all other spells and magical effects.

It is clear to me that Tiamat can simply walk or fly through a wall of force due to her immunity, unless the wall was upcast so as to be at least 7th level, in which case it would be a barrier to her.

However, it is not clear to me whether her breath weapon counts as 'her'; that is, whether the damaging effects that she can produce as breath weapons are included as Tiamat being immune to the spell, and would thus be able to pass through a non-upcast wall or not.

If she picked up a stone a threw it at the wall, I would expect the wall to stop it; clearly the stone is not her, even if she did impart its motion (then again, I don't think it is intuitive that a magical bow allows a non-magical arrow to fully damage a creature with resistance to non-magical damage. I agree that it does, I just don't think it is intuitive).

Her breath weapons seems to lie somewhere between a thrown stone and her own body - her breath weapons are more 'her' than the stone - but are they enough her to pass through like her body would?

Nobody the Hobgoblin
  • 112,387
  • 14
  • 326
  • 684
Kirt
  • 50,327
  • 7
  • 121
  • 276

3 Answers3

12

No.

Let's consider a related question. There's an adult blue dragon, and it breathes lightning at a wall of fire. This wall says:

...A creature takes [the] damage when it enters the wall for the first time on a turn or ends its turn there.

Does the blue dragon's breath weapon cause it to take damage when the breath weapon enters the wall?

Okay -- what about a prismatic wall? Even Tiamat can't ignore this 9th level spell. The spell says:

When a creature attempts to reach into or pass through the wall, it does so one layer at a time through all the wall's layers.

If Tiamat uses her breath weapon on this wall, does that count as "reaching into it", such that she gets affected by the seven layers?

Based on these examples, I think we can agree that a dragon's breath weapon is not a part of the dragon.

You're welcome to house-rule this if you want. (Personally, I wouldn't. You mentioned in a comment that Tiamat could just stick her head through the wall before using her breath weapon, and that seems much more cinematic to me.)

Dan B
  • 89,473
  • 14
  • 195
  • 337
  • Interesting thought experiments. In the absence of actual rules or official rulings, I find these case studies very useful in guiding my thinking. – Kirt Oct 17 '22 at 00:42
  • 2
    @DanB I think the difficulty is that we do not know what "immunity to spells" means. The breath weaopn may not be part of the dragons body, but does that mean that spells cannot affect the body, or does it mean that spells cannot more broadly interact with it? – Nobody the Hobgoblin Oct 17 '22 at 04:33
  • 3
    @GroodytheHobgoblin I think we are running into an implied statement here. If a cleric casts a shield of faith on the fighter (+2 to AC) does that mean the monster ignores the buff spell, even though the spell never targeted Tiamat? Immunity to spells means they can't be targeted or recieve damage, but what about wall spells? Wall of stone for example? And Wall of force is an intangible wall made of Force, not specifically magic according to the spell description. But arguments could be made either way. – Play Patrice Oct 17 '22 at 04:49
  • 3
    @PlayPatrice Beware that the wall made by the Wall of Force spell is magical, because it is a spell: see the Sage Advice Compendium about checking if something is magical or not. – Eddymage Oct 17 '22 at 07:17
1

No, because if the breath weapon were to be an extension of any dragon, it would be magical, but it isn't.

Dragons are magical, but their breath weapons are not, so their breath weapon is not an extension of the dragon — otherwise, it would be magical. We can infer so from the SAC V.2.5, p.20:

[...]or use another feature of the game that protects against magical or nonmagical effects, you might ask yourself, “Will this protect me against a dragon’s breath?” The breath weapon of a typical dragon isn’t considered magical, so antimagic field won’t help you but armor of invulnerability will. You might be thinking, “Dragons seem pretty magical to me.” And yes, they are extraordinary! Their description even says they’re magical. [...]

If we consider Tiamat's dragonhead a dragon, it follows that her dragonhead's breath weapon is not an extension of her. Even should we not consider her to follow the same rules, this ruling is as close as it gets to a ruling on whether a breath weapon is an extension of the creature that uses it.

Eddymage
  • 28,645
  • 3
  • 76
  • 150
Akixkisu
  • 19,584
  • 13
  • 80
  • 138
  • 3
    By the SAC's logic, dragons are magical because their description says they are, "Dragons are also magical creatures whose innate power fuels their dreaded breath weapons and other preternatural abilities." Interestingly, their claws are not magical - compared to, for example, an arcanaloth. So Tiamat herself can move through a wall of force but she cannot attack through one with her claws and bite because these parts of her are not an extension of her? This is an interesting line of reasoning but ultimately not satisfying. – Kirt Oct 18 '22 at 14:15
  • To be clear, I agree with your reasoning; I just don't like where it leads, which is the fault of the SAC's argument, not yours. – Kirt Oct 18 '22 at 14:22
  • @Kirt I agree, it is utterly unsatisying. At my main table, I would try to play it in whatever way feels most immersive in that encounter (something we agreed on in session 0). – Akixkisu Oct 18 '22 at 15:43
-5

This is up to you as the DM

This is one of the cases, where there are no clear-cut rules to quote, so ultimately it will be up to the DM. The instances where immunity is mentioned in the PHB and DMG are all discussing immunity to a damage type, not to spells. Without formal definition of what immunity to spells means, you will have to define that.

We do not know if immunity to spells means that spells cannot affect the creature's body or mind, or if it means the creature ignores effects of the spells, as if they did not exist. If we did know, we could conclude with certainty that only the body can pass here, or that the wall has no effect.

If you follow the interpretation that spells have no effect, then the wall will not block her breath weapon. Following this logic will also have other consequences, such as Absorb Elements not working: if she can ignore these spells, their damage will not be affected or reduced by resistance granted by the spell.

Nobody the Hobgoblin
  • 112,387
  • 14
  • 326
  • 684
  • 2
    Agreed that Tiamat is supposed to be the epic final fight - and I intend to use her that way. Even if I ultimately decide to have a normal WoF block her breath though, at best it will buy the party time. She is gargantuan and too large to be placed in a wall herself. The party may use a wall to protect their casters from her breaths, but she can dash-fly 240 feet, so it won't be long before she simply crosses through the wall itself and breathes on them. In fact, she would likely stick a head through, breathe, and then pull it back out so the wall protected her. – Kirt Oct 16 '22 at 07:36
  • @Kirt congratulations, you found an example where pulling out is not a horrible idea! xD – PixelMaster Oct 16 '22 at 09:23