Using Daern's Instant Fortress as a portable meteor

Question

First, some context: Some time ago I played a 12th Level Bard in an online oneshot that started us out with a choice of X magic items of Y rarity. Amongst my picks was Daern's Instant Fortress, which was used under the assumption that, once dismissed the Fortress turns into a small cube, ready to inflate again. Near the end of the session there came a point where we made our way down a very wide circular stairwell that broadened as we descended and seemed to extend downward for several hundred feet. Down below, in the relative center was a gargantuan (4x4) big bad.

The second we were made aware of this I said the following (roughly summarized):

"I want to run back up the stairs, palming Daern's and a Plate. Once I'm at a level that has a diameter of roughly 60 feet I want to summon my mage hand, put a plate from my mess kit (I had an explorer's pack with me) on it and place Daern's Instant Fortress on top of it. I command the hand to fly as close to the center of the stairwell. Once it's there I utter Daern's command word."

Now, obviously the desired outcome of this would be that the big bad down below would be caught off guard and crushed by what must be several tons of enchanted adamantite. I didn't mind that a drop from that height may destroy the item (I consider a falling Fortress a siege weapon upon itself and whatever it strikes). Other party members already used their magic items in wacky ways, so I didn't fully catch anyone off guard with this. It did end up turning into a 10-ish minute long argument on whether Daern's is:

A) On the "ground" while it is flat on a plate held in the air by a magic floating hand

and

B) Whether the fortress was even affected by gravity

For A) we quickly stumbled on this question on here and reasoned that for our purposes the plate as a solid surface would suffice for the cube to expand. We agreed that the item would not check if it had a 20x20 area of air around to expand onto and instead be content by having one side flat on some surface. The item's description mentions no such thing so it shouldn't check for that.

Regarding B) the GM and two players argued that "[...] its magic prevents it from being tipped over.[...]" in the Fortress's description implied it was not affected by gravity and would be fixed to its location of origin.

Now, I personally believe that the magic enforcing an upright position does not keep the Fortress from being affected by gravity's pull. There's nothing explicitly stating that effect and as such standard "laws" should apply. Not wanting to turn this into a full out argument, I settled for that interpretation and continued playing.

We had fun throughout the final fight, but the differing opinions on the fortress left me a bit upset.

Going by what is written in the item's description, could you drop a fully expanded Instant Fortress from a great height?

Answer 1

The contentious part of this question is whether a plate in mid air can be considered 'ground'.

The Instant Fortress description says:

You can use an action to place this 1-inch metal cube on the ground and speak its command word.

I'd rule that a plate in mid-air could not be considered ground.

You've linked to another question on this site, to support your assertion that a plate could be considered 'ground'. However, in the accepted (and most popular) answer to that question, Vladislav Martin says:

'ground refers broadly to any solid continuous, contiguous surface on the planet.'

Which actually seems to disagree with your assertion completely.

While it's possible that a DM might rule in your favour (certainly for Rules As Fun reasons), probably most would rule, RAW,that a floating plate could not be understood as 'ground'.

That said, you were right, once in the air, there's no reason the fortress wouldn't be subject to gravity.

The Instant Fortress description also, says:

'magic prevents it from being tipped over'

But this doesn't logically imply that it couldn't fall - though it could be argued that it might fall in an oddly straight manner, landing straight and stuck like a dart in a dart board.

However, there is already a way to use this as a weapon, RAW

Each creature in the area where the fortress appears must make a DC 15 Dexterity saving throw, taking 10d10 bludgeoning damage on a failed save, or half as much damage on a successful one.

So, why not simply throw the unexpanded fortress down and then expand it once it lands, on the ground, next to the BBEG?

If it can't be a meteor, it's still a fairly impressive grenade.

At the very least, this is a great compromise option if the DM won't let you do what you really want to to.

Answer 2

Rules as written, it doesn't specifically say that it can't fall, which means that it can (otherwise, you could make any object hover by pointing out that this particular item doesn't specifically say that it is affected by gravity).

Answer 3

It's very specific in its verbage that you must place it on the ground as an action and then speak it's command word. The plate is not the ground. I personally would rule that if you are placing it somewhere where it could fall immediately after being expanded, it does not constitute as ground.

You could use it as a very effective ambush tool for weak and/or dumb enemies. For example, just leave it on the ground where you know an enemy is going to walk. When it notices the cube, it will walk over to investigate. You then shout out the command word and boom, it expands, dealing the damage the descriptions says it does.

Throwing it or levitating it is not how the spell specifies deploying it. You must place it on the ground. Mage hand still works as long as you place it on the ground. You cannot throw it on the ground as some users suggest doing like a grenade. I know irl you could argue that this would conceivably work, but this isn't real life, its a game with defined conditions that must be specifically met.

Rule of cool is fun and all as long as its not breaking the game. Shenanigans with instant fortress that violate its conditions most definitely qualify as breaking the game.