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

[davethebrave]

Absolutely allow it. Though may have it scaled down to a lesser version on smaller vehicle. This is magic/fantasy after all. I would rule if it were a wagon, the wagon would need to be of the highest quality and expense. A ship would need to be equally embellished with the highest grade materials.

 

[CleverNickName]

This thread is a blast from the past. Welcome to the forums, @davethebrave !

 

[Samloyal23]

Absolutely allow it. Though may have it scaled down to a lesser version on smaller vehicle. This is magic/fantasy after all. I would rule if it were a wagon, the wagon would need to be of the highest quality and expense. A ship would need to be equally embellished with the highest grade materials.

Yes, the whole vehicle has to be enchanted to make the spell function, so treat it like a magic item.

 

[UngeheuerLich]

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".

The wall of force sweeping everyone from board actually makes sense... but yes, it is a really difficult decision.
Maybe have some kind of magic inertia effect. If you are moving for for a while on a big vessel, your spell effects can be and are usually bound to it Otherwise a lot of immobile effects are all moving when they should not.
As long as you do it below deck, I guess there is no question at all. Above deck, for your wall of force, the question is, what happens if you cast iton the open sea. Here I would go with static. Aven more problematic is if a part is on the ship and the other part not.