Welcome to "Inter-planar Shenanigans" general. Post anything related to that and you should be fine.
Specifically, dealing with being in a campaign that requires several teams working across several planes.
I've got some of my own stuff thought up, but feel free to make your own suggestions... and maybe help me figure out the stuff I don't know about.
Communication:
Anyone dealing with having to perform quests across multiple planes is going to have a hard time of it if one can't communicate with each other. And sometimes, not every character can be a wizard, or have one nearby. Not to mention, the main ways to communicate across planes can be quite taxing on a wizard's daily spells
The best solution seems to be to create an item that can cast those spells at will. Which optimally would be things like Sending or Scrying... or both (possibly using sending to act as a ring tone to remind the one at the other end not to make a will save.) Of course, the main thing is to make them able to do those kinds of spells pretty much "At will".
I have no idea how the rules go for creating such an item, or how pricing it would go. So feel free to mention how that would work.
Item Delivery:
So, there's also the question of sending items to each other across planes. Say you need to get a new set of gear to another character who got theirs destroyed, but going in person would be a waste of time and effort.
The best I can come up with is a kind of variant of secret chest; where instead of one replica, there are several; or perhaps another magic item that acts as both the focus and the spell caster; which could be synched up with each other through a process similar to sending.
In fact, it could be put on the same item as the communication item.
Incomplete Tardis:
Need an abode that can Travel across the planes? And possibly bigger on the inside maybe? Although time travel probably isn't going to be included RAW just yet, you can do a fair bit. But considering my settings usually treat Time and planar travel as the same thing, using the same spells, that doesn't matter.
I presume a good solution would be to use another variant of Secret chest. And Create a Demi-Plane, and have a permanent planar portal placed inside the chest. And from there you can essentially move the portal where-ever you need by moving the chest. And since the chest can be sent to the ethereal realm...
The next question is how to get it go go other places than the ethereal realm. I guess the best way I can think of might be to use the recall for the chest to sort of bring it into the demi-plane it links to. And from there have a item that you can use to make a temporary gate, with which you use to kick the chest out of.
Even without the whole planar traveling thing, I'm sure that having a portal to your demi-plane that you can move around is useful.
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Anyone with ideas that can make an adventure with teams in multiple planes easier should definitely post them.
