I had an idea the other day, but need some clarification to see if it would work. We all know that putting an item that creates an extradimensional space inside of another such item causes a big boom. However if a creature that is polymorphed was holding such an item and is placed in another such item, would the boom happen immediately or after polymorph ends?

The question is would the bag instantly implode, or would it wait until polymorph ended. If it waits until polymorph ends you have created a grenade. Since you can choose to end concentration at any point.

I would say that you have a delay, but that's a pretty expensive grenade destroying 2 magical items.

When you merge things into form they are no longer in effect, as if they aren't there. Magical armour you wear no longer grants protection or magical benefit. You treat it as if its no longer present.

I would say it would be the same with the Bag. Once merged it's gone, so you're free to enter the dimensional space. If you revert while inside then there is a boom.

Seems a very expensive way to get rid of somebody.

Worth noting we are saying "boom" and "grenade" but the bad event of mixing your interdimensional spaces just sends things to the Astral Plane (or Sea, whichever nomenclature you prefer: it's the same place). If the beings taken away there have a Plane Shift or Gate spell they can just bamf right back. Even those that cannot teleport can also return eventually - the Astral Plane is littered with portals and means of travelling to other realms, it's actually a means of interplanar travel. So, anything you send away could eventually find a way back.

So, destroying two bags of holding just to temporarily and harmlessly get rid of somebody seems like a bit much. I used to think it was a great way to "win" a situation until reading more on the Astral Plane and how easy it was to get back. It's really not worth it.

Quote from Cyb3rM1nd >>

When you merge things into form they are no longer in effect, as if they aren't there. Magical armour you wear no longer grants protection or magical benefit. You treat it as if its no longer present.

I would say it would be the same with the Bag. Once merged it's gone, so you're free to enter the dimensional space. If you revert while inside then there is a boom.

Seems a very expensive way to get rid of somebody.

Worth noting we are saying "boom" and "grenade" but the bad event of mixing your interdimensional spaces just sends things to the Astral Plane (or Sea, whichever nomenclature you prefer: it's the same place). If the beings taken away there have a Plane Shift or Gate spell they can just bamf right back. Even those that cannot teleport can also return eventually - the Astral Plane is littered with portals and means of travelling to other realms, it's actually a means of interplanar travel. So, anything you send away could eventually find a way back.

So, destroying two bags of holding just to temporarily and harmlessly get rid of somebody seems like a bit much. I used to think it was a great way to "win" a situation until reading more on the Astral Plane and how easy it was to get back. It's really not worth it.

 "Easy to get back" is not accurate. If they have means of planar travel, sure, but if they are relying on portals to get back, it may take years or longer if they make it back at all. The portals are random and if they wind up in an outer plane there are all manor of things that might prevent them from coming back to the material. You are right that it is an expensive and complicated means of getting rid of something with no guarantee though.

Quote from DxJxC >>

 "Easy to get back" is not accurate. If they have means of planar travel, sure, but if they are relying on portals to get back, it may take years or longer if they make it back at all. The portals are random and if they wind up in an outer plane there are all manor of things that might prevent them from coming back to the material. You are right that it is an expensive and complicated means of getting rid of something with no guarantee though.

 
I apologise, perhaps I should have clarified I was going by the Dungeon Master's Guide where it is detailed that you can always find a portal to the plane you want to go to within 1d4x10 hours of travel and there is a rare chance of a psychic wind that has a small chance to send you somewhere random or add a maximum 30 hours of travel time. I'd consider that since most of the time you just travel 10 to 40 hours before finding the exact portal you need to get to where you're going this is rather easy.

So what prompted this is a tournament against other players, where some of which have a bag of holding. The people removed by this means have a max of 10 minutes to return. So it is quite effective in this scenario, where I only lose one item, but remove two enemies.