Demiplane: Plane and Simple
Spell Level: 8
School: Conjuration
Casting Time: 1 action
Range: 60 feet
Duration: 1 hour
Components: S
You create a shadowy door on a flat solid surface that you can see within range. The door is large enough to allow Medium creatures to pass through unhindered. When opened, the door leads to a demiplane that appears to be an empty room 30 feet in each dimension, made of wood or stone. When the spell ends, the door disappears, and any creatures or objects inside the demiplane remain trapped there, as the door also disappears from the other side.
Each time you cast this spell, you can create a new demiplane, or have the shadowy door connect to a demiplane you created with a previous casting of this spell. Additionally, if you know the nature and contents of a demiplane created by a casting of this spell by another creature, you can have the shadowy door connect to its demiplane instead.
Review by Sam West, Twitter: @CrierKobold
We all have that special place: our little corner where we can go to be alone and just vibe. What if you could have access to that space… anywhere? What if you could transform that space into the perfect zen garden for relaxing meditation? What if that space also could contain massive amounts of stolen explosives or other dangerous objects, free from prying eyes? What if you could transform it into a prison for which there is no escape, an endless extraspacial holding cell only practiced archmages can break? I think I’m losing this comparison…
Demiplane is what an 8th level spell should be. This spell is simple, flexible, and has just enough restraints on it to make planning out and using it an interesting puzzle to solve. It basically allows for you to create a room that exists where you want when you want it to.
At its face value there isn’t a lot here. You make a room and a gateway to that room that lasts an hour, that's it. The door is too small for large or larger creatures to get in, and the space is just stone or wood. With how simple it is, you will be amazed at the sheer quantity of problems this helps solve.
Need a safe place to hide out for a few days? Demiplane! Have you captured a powerful warlord, and need them alive in a few weeks? Demiplane! Need to stash an artifact to avoid magical detection? Demiplane!
Keep in mind, without other means of planar travel Demiplane can permanently trap you in an endless loop of demiplanes, but alongside plane shift or astral projection, Demiplane can act as a great tool for safe, uninterrupted long rests.
The hour-long duration for the door does make its practical applications challenging. If you want to trap something, you have to figure out how to contain it in the Demiplane until the door disappears. If you can’t hide the doorway for an hour, Demiplane doesn’t do a great job hiding people from danger. It is just an action to open a door, though, meaning if you’ve trapped 10,000 angry hornets in one you can functionally summon them by opening up the doorway and letting them loose. Consider creating an underwater Demiplane, then opening that door when you need 900 square feet of water on command. These all just scratch the surface of its applications.
Where the spell shines brightest from a world building perspective is using it to open other creature’s Demiplanes. A villain obviously can find utility in extradimensional holding areas; requiring the players gain access to this kind of magic to open them alongside needing to find precise details on the nature of each builds an easy quest to explore in the upper tiers. Pair it with clone, get real wild.
Demiplane is not only is a flexible tool for exploring the world and creating crazy solutions to niche problems, it doubles as an deep well of ideas for DMs to play with in creating labyrinths of extradimensional spaces and four dimensional puzzles that highlight why D&D is so amazing for so many people. If you can, learn Demiplane. You will find a weird use for it, and everyone will love it.
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