The Onyx Key is a powerful artifact that serves as the focus and control mechanism for the vast dimensional energies collected by the xiomorn facility called the Onyx Citadel. The citadel itself maintains a complex network of extradimensional tunnels known as the Stone Roads—once used by the xiomorns to travel across the Plane of Earth—and allows this network to bridge into other planes, granting its user the power to move resources or entire armies.1
Eight shards of black crystal grow from the Onyx Key's base, which can easily be broken off. If an onyx shard is plunged into natural earth or stone, it begins rumbling and grows into a 30-foot spire of translucent black stone with an archway in its base. The tower's archways can be commanded to open an extradimensional tunnel to the archway of any other onyx tower on the same plane. A Stone Road opened between two towers is typically a 100-foot stone tunnel, but as with many elements of xiomorn magic this is far from certain, and gates may occasionally run far longer, with smaller side passageways leading off into the unknown.
A crystalline matrix—a network of circles and imbedded stones—embedded in each spire may be manipulated to open and close the tower's connection to other towers, destroy it, or restructure the tower's design. A tower's footprint cannot exceed 120 feet on a side, and cannot grow taller than 80 feet.
In addition to the eight black shards, a single shard of sardonyx grows from the Onyx Key's base. This shard cannot be used to grow a tower, but instead may be installed in an existing tower to augment its power, allowing it to open a Stone Road to the Onyx Citadel itself, or connect to onyx towers on other planes.
Whoever possesses the Onyx Key itself may mentally destroy an existing onyx tower, but cannot destroy a shard that hasn't yet been transformed into a tower, nor the sardonyx shard if it hasn't been installed in a tower. Once a tower is destroyed, its corresponding onyx shard regrows from the Onyx Key over the next month.1
The eight onyx shards of the Onyx Key must be planted in the eight ends of the Stone Road, stretching the device's magic thin, while the Onyx Key itself is cast into the Storm of Fangs on the Plane of Air.1
While the Stone Road predates the Onyx Key—the Onyx Citadel and other hubs of xiomorn science already capable to opening gates to this network—the artifact gave its ancient creators the gift of mobility and the power to leap the dimensional barrier with ease, expanding their experimentation to new worlds. As the xiomorn withdrew from Golarion, they left the Onyx Key, alongside many other treasures, in a sacred stronghold in the Darklands layer of Orv.
The artifact entered the modern history of Golarion when it was discovered by the dwarven explorer Kraggodan, who followed strange whispers in the earth to the vast treasures the xiomorn left behind. Using the onyx towers as a series of ever-advancing strongholds, Kraggodan and his clan completed their Quest for Sky swiftly and with minimum casualties—most notably Kraggodan himself, who died defending his people from the orc hordes—and the clan named the city they founded in honor of their late savior. Once settled in, the dwarves began to experiment with the Onyx Key in hopes of understanding its powerful magic, and instead opened a Stone Road to the Vault of the Onyx Citadel, allowing all manner of outsiders to flood through and devastate their population. Wary of a similar tragic mistake, they sealed the artifact in a sacred vault dedicated to their people's history, safely locked away from curious hands.
And there the Onyx Key stayed for thousands of years, largely forgotten by all but a few, until it was stolen by the hobgoblin warlord Azaersi, precipitating the events of the Ironfang Invasion.1
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- ↑ 1.0 1.1 1.2 1.3 Crystal Frasier. (July 20, 2017). The Ironfang Resolution, Paizo Blog.