Keystone of Creation
Wondrous Item, artifact (requires attunement)
A keystone of creation is a piece of the Stone of Creation, usually between 6 to 10 inches on a side, and can be rough-hewn or cleanly cut and polished by a mason attuned to the Stone of Creation.
Random Properties
A keystone of creation has the following random properties:
- 1 minor beneficial property
- 1 beneficial manifestation
- 1 detrimental manifestation
Extradimensional Places
You can use the keystone to conjure an extradimensional space such as Mordenkainen’s magnificent mansion. The easiest way is to simply cast the spell using the artifact’s power, which requires no spell slots or material components. Each time you cast a spell with the artifact, the subsequent casting replaces the prior one. For more detailed control of a conjured demiplane or extradimensional space, see “Construction Details.”
Raising Structures
You can use the keystone to conjure a physical structure on the Material Plane. The easiest way is to simply cast the mighty fortress spell using the artifact’s power, which requires no spell slots or material components. Each time you cast a spell with the artifact, the subsequent casting replaces the prior one. For more detailed control of a conjured demiplane or extradimensional space, see “Construction Details.” Locations conjured by keystones cannot become permanent through repeated spell castings.
Connected Spaces
You can use multiple keystones to create larger spaces, whether adjacent to each other or even interlinked. You can even combine structures on the Material Plane and extradimensional spaces this way. If you are attuned to one keystone when you attune to a second keystone, the keystones combine to become a single artifact (utilizing a single attunement slot), combining their features and their fates forevermore. You cannot attune to, and thus combine, more than three keystones at once.
Destroying a Keystone
A keystone is an artifact in its own right and impervious to most damage, but a disintegrate spell is sufficient to destroy an unattuned keystone.
After it has been attuned at least once, a given keystone requires attunement to maintain its magical power. Otherwise, its creations on the Material Plane gradually rot and decay over 1d12 + 1 days, and a demiplane relying on the keystone collapses over 1d20 + 10 minutes. Additional destructive forces like fire may hasten the destruction. A demiplane created or upheld by a keystone ejects all creatures within it to their home planes when it collapses.
When a keystone’s creation is fully destroyed, the keystone becomes an inert, powerless rock. If the Stone of Creation is destroyed, all its keystones break attunement, lose all magical properties, and their creations decay or collapse to nothing.
If it reaches the Elemental Chaos or is struck by a forked, metal rod attuned to the Elemental Chaos (as per the plane shift spell), a keystone is destroyed.
Construction Details
You can customize a keystone’s creation with cosmetic details you can imagine. You can also rearrange the floorplans and structural details of your creations as follows.
Demiplane Design
With a single keystone, you can conjure an extradimensional space in the shape of a dome or pyramid, up to 1 mile on each side, with whatever terrain you wish. The edges of this space are solid and impassable but may be invisible, so that your space can appear to go on forever if you wish. With additional keystones, you can add an additional square mile to your creation, adding or combining terrain types.
Each square mile can include a single structure up to the size of Mordenkainen’s magnificent mansion, with all the attendant servants and feasts, or any number of smaller structures that together equal a magnificent mansion in total area.
You cannot create flora or fauna that deal damage or otherwise harm creatures. If you create cliffs, waters, or other natural features, however, creatures in the space might fall, drown, or otherwise be harmed.
Physical Structure Design
With a single keystone, you can create a structure akin to a mighty fortress with the added flexibility to customize that fortress not only for cosmetic details but for substantive effects. With a single keystone, you can rearrange the walls, open spaces, floors, doors, and other features of the mighty fortress provided you do not exceed 150 10-foot-wide cubes of interior space. Your fortress can reach across a creek, river, or other waters. It can take reckless or even dangerous shapes to include deep pits, flooded chambers, and so on. Your design, once conjured, is not guaranteed to be capable of supporting its own weight or surviving the stresses of attacks, weather, or time.
You may post any number of your structure’s servants as guards, if you wish. They have statistics identical to an unseen servant with the addition of a passive Perception score equal to your own, though you cannot perceive through their senses. The servants can ring bells or otherwise manipulate the environment to raise an alarm.
Manifestations
Each place or structure conjured by a keystone of creation has special, unforeseen manifestations that affect its makeup and appearance. Some manifestations are beneficial, some are detrimental. These manifestations change each time a keystone is used to conjure a structure or place. The DM may roll or choose from the following tables, or devise unique manifestations based on the specific creations being conjured.
Source: Adventures in the Forgotten Realms: A Verdant Tomb p. 12, Adventures in the Forgotten Realms: Deepest Night p. 14, Adventures in the Forgotten Realms: Deepest Night p. 13