What Happens When The Ground Drops from Under a Tiny Hut?

Question

During a recent game, our party came under attack by a Big Bad. The DM introduced it in a suitably epic way- the area we were camping on sank 10 feet per round into a massive pit, until there was room for the Gargantuan creature to stalk over and begin pounding us into the dirt. After one round of attacks flat out killed the party's pet NPC paladin and dropped the other front-line fighters to half-strength, it became clear that this was a fight we were intended to run from.

We did not. In fact, we won, though I'm not sure we should have.

Our defense relied heavily on a casting of Leomund's Tiny Hut, which had already been in place for two hours when the fight began. Per the spell:

A 10-foot-radius immobile dome of force springs into existence around and above you and remains stationary for the duration. The spell ends if you leave its area.

Creatures and objects within the dome when you cast this spell can move through it freely. All other creatures and objects are barred from passing through it.

Now, we interpreted that to mean that we could fire missile weapons through the hut with impunity, and that we could even make melee attacks through the hut, as it lists no thickness for the dome and our characters and their weapons could "move through it freely." This strikes me as a bit OP for a third-level spell, but the casting time implies that it isn't normally intended to be used in combat anyway. I invite comments on the legality of that tactic, but my real question is this:

Should Leomund's Tiny Hut have failed immediately?

I am aware that previous questions have addressed whether Leomund's Tiny Hut works on a moving surface, but this question differs in that the surface in question was normally stationary. This wasn't a ship or an iceberg moving- this was the ground beneath us suddenly sinking. Should we have treated the ground as though the hut was cast on a moving area, or would it have been more accurate to treat what happened as slowly falling out from under the hut? If the latter is the case, and the hut is a dome, I believe the spell would have ended the moment the last of the caster passed under the bottom edge of the dome. Does this sound correct?

Answer 1

If the caster falls, the spell ends once the caster is no longer in the original area.

While the linked questions have some debate about whether or not the dome moves with its surroundings, the text is clear that if the caster moves out of the original "stationary" position, then the spell will end:

The spell ends if you leave its area.

Therefore, as formulated in your question, the hut would have disappeared once the original caster was no longer in that space.

I agree with the linked answers that there is no clear definition of "stationary," which leaves the crux of your question up to a DM's judgment call. As a DM, I would have ruled that the hut does not fall because there seems to be a clear "stationary" reference frame based on your description of the fight: the rest of the environment that isn't moving. It's worth noting that the range of the spell is "self," and since the hut obviously doesn't move with the caster, the location of the hut is where the caster was at the moment the spell was cast.

While other DMs could reasonably rule otherwise, it opens up a lot of judgment calls--how big does the piece of moving ground have to be? If the caster digs up the ground and moves it around, could they move their hut? In this case, where you're on solid ground, it seems easier to say that it doesn't move at all.

Leomund's Tiny Hut has a floor

However, the scenario in your question could have only happened if the players willingly fell out of the hut, because Jeremy Crawford tweeted that the intent is that it has a floor to stand on:

Leomund's tiny hut does have a floor, Mr. Crawford (read your own book). The spell's range entry says the effect is hemispherical.

Thus, even though the ground fell out from under you, you could have still stood on the floor of the hut.

As for balance concerns, many Big Bads often have some way of dispelling magic. Leomund's Tiny Hut, a 3rd level spell, would be automatically dispelled. If the gargantuan attacker were only a physical attacker, it could have simply left and waited out the spell's duration out of range of your attacks--you can't pursue it, after all, without leaving the protection of the hut.