D&D 5E Mordenkainen's MOBILE Mansion? Opinions wanted

[Mouseferatu]

So, there's no RAW answer to this, and that's fine. I'm looking for opinions and repercussions.

If someone were to cast Mordenkainen's magnificent mansion while aboard a vessel (such as a ship), would you permit the entryway to move with the vessel? Why or why not?

 

[AaronOfBarbaria]

I permit effects which are stationary to be mobile by way of a vehicle. The reason is simple; I think "On the poop deck" or "In the captain's quarters" are still those same locations no matter where the ship may be.

Just like "In the wizard's tower apex" is the same location no matter whether that tower is built in a world that rotates and/or orbits a star.

 

[Mouseferatu]

Do you interpret that way for all vehicles, or only of a certain size? If the spell can be mobile on a ship, could it be mobile on a rowboat? In the back of a horse-drawn cart?

(I'm not trying to trip you up; I'm honestly trying to work out the repercussions of ruling either way.)

 

[Rabbitbait]

I'd follow a strict interpretation of the rule of cool in this case. On a ship feels epic, so yes. On a cart is a bit sad, so no.

WWTFDIHWM - What would the Fonz do if he were Mordenkainen.

 

[AaronOfBarbaria]

Do you interpret that way for all vehicles, or only of a certain size? If the spell can be mobile on a ship, could it be mobile on a rowboat? In the back of a horse-drawn cart?

(I'm not trying to trip you up; I'm honestly trying to work out the repercussions of ruling either way.)

Any vehicle of sufficient size for whatever spell effect is in question. So for Mordenkainen's mansion, any structure that can fit the 5' wide and 10' tall portal is fine, such as "our cart" or "our rowboat" being the location assuming each is at least 5' wide.

Personally, I think the repercussions are a choice between the following two options:
A) Vehicles aren't suitable locations because they are "mobile", and thus that the spells work at all is inherently inconsistent because a truly immobile effect would appear to travel away from the caster at the planet's rotational and/or orbital velocity by staying where it was cast rather than traveling with the "vehicle" that is the planet.

B) The spell can be applied consistently, but certain choices of location appear to be more mobile than others because they are moving about within the "vehicle" that is the planet.

 

[Inglorin]

I'd allow it but would let the mansion "roll in the waves" or something like that. Being sea sick while hiding in the mansion could be cool. Walking around in my mansion, while the donkey that pulls the cart stumbled on a tree branch on the road... priceless.

 

[Fanaelialae]

I'd allow it. Even ignoring the moving planet argument (which might not be true in a fantasy setting if everything rotates around the "Earth"), it's the easiest way to handle it. Having every spell effect fixed rather than mobile might result in wonkiness (creating a Wall of Force to sweep everyone from the deck of a ship). If it's done on a case-by-case basis, players will never know what to expect until the DM makes a firm ruling, plus that could be a lot to remember. Will Evard's Black Tentacles move with a mobile platform or is it fixed? If all spells are relatively mobile, ship combats play out similarly to land combat, without the need for rulings on where and how far fixed spells will "drift".

 

[Dausuul]

So, there's no RAW answer to this, and that's fine. I'm looking for opinions and repercussions.

If someone were to cast Mordenkainen's magnificent mansion while aboard a vessel (such as a ship), would you permit the entryway to move with the vessel? Why or why not?

Yes, I would.

In general, I feel that when a PC gets a new spell, the spell should work as advertised absent a compelling reason for it not to. In a campaign that took to the sea, MMM would become near-useless for its intended purpose if it couldn't move with a ship. It would gain a new use as a combination anchor/battering ram, and I'm all for players finding creative uses for spells, but picking up MMM represents a significant investment - high-level spells are hard to come by - and I think the player should get what s/he paid for.

As far as the limits of vehicle size, I'd probably rule that on a spell-by-spell basis. For MMM, I would allow it for any vehicle big enough to physically accommodate the door. Yes, that means you can build a 7x4 wooden frame, cast MMM on it, and tote the frame around in the back of a wagon. I kind of like that idea, actually.

 

[FormerlyHemlock]

So, there's no RAW answer to this, and that's fine. I'm looking for opinions and repercussions.

If someone were to cast Mordenkainen's magnificent mansion while aboard a vessel (such as a ship), would you permit the entryway to move with the vessel? Why or why not?

No. Because it's fixed w/rt the local gravity field/inertial reference frame. Because I have to make a ruling and that one is both reasonable and easy to adjudicate, and easy to imagine why it works that way in magical-physics terms.

 

[S'mon]

I'd allow a 'cabin door' on a ship that opens into a Magnificent Mansion. I would not allow 'tote around a chintzy wooden frame'. I might conceivably allow a gyspsy type wagon's door to open into a Magnificent Mansion.

If I allow this then interior of the MM will be subject to same rolling/movement as its link portal.