Accorion, the Halls of Black

Credits to Emanuel Mendez from Artstation for the haunting cover art!

Origin plane of lycanthropy, vampirism, and the secrets of necromancy, of demons, demonic blood, and chaos, prison plane of Narvox, the King in Black himself, Accorion was designed to be the prison of all the vile things Yamma and Alindr hoped to keep from the rest of Yophas. Much like Xeccamund, the Halls of Black were created to hold those evils that couldn't be fully eradicated but could at least be withheld from the multiverse. And though it was imperfect, Accorion did its job through much of the Age of Rebirth. And when it failed, the Reckoning began -- indeed, when Accorion was shattered, chunks of it rained down as meteorites across all of Yophas, leaving small deposits of adamantine, pitchcopper, and dragon titanium, the strongest metal in Yophas.

Though some of its prisoners managed to trickle out over the course of millennia -- like when vampirism found its way back to Emaxus, and demons found their way to Mathrak -- Accorion largely kept the evils it was meant to keep at bay, at bay. But when Narvox grew powerful enough to shatter his chains, he shattered the very plane that held him. Records show that, before the Reckoning, Accorion was a land of infinite layers of prisons, connected by darkened halls and stone doors, thus the moniker "Halls of Black." When Narvox broke free, he shattered Accorion itself and forever ruined the foundations of its prisons. The realm of infinite, ordered layers ranging from world-sized demiplanes to tiny prison cells became a seemingly endless cluster of floating debris.

Ranging from planetoid-sized chunks of broken halls and shattered demiplanes to shifting and changing planar prisons that seem to blink in, out, and through our reality. Most laws of spacetime have ceased to function properly in Accorion. Different "domains" functions under entirely different rules, and though the different portions of Accorion may seem to be of certain sizes or compositions when they're seen from Ipacia, those observations rarely hold true upon closer investigation.

A Broken Plane

Of all the Divine Planes, Accorion is the only one that no longer functions how it was intended in the slightest. Though the natures and constituents of almost all the planes have changed since the Reckoning, Accorion was literally shattered. It has become a labyrinthine and segmented realm of floating, disparate chunks of planar stuff, all of which are fought over and within by constituents ranging from ancient vampires to primordial demon lords.

As a DM, let your mind truly go wild with adventures in Accorion -- almost anything is possible. If the players come by way of Ipacian navigation, they may see a simple, asteroid-esque chunk of black rock with pieces of dark stone structures jutting from within, but upon landing their vessel and making their way inside discover that its actually an infinite sea of glass. Ancient and innumerable evils were imprisoned here, and Narvox set them all free, either on accident or by design.

As a player, have a good time and expect the completely unexpected. Accorion is a madhouse packed with Yophas' worst nightmares, many of which want each other dead and all of which want you dead -- probably. (I don't want to rule out parlaying and alliances, but you get my meaning.)

Inhabitants

Countless corrupting and insidious evils were imprisoned in Accorion, and those and more roam its shattered remains today. Vampires, lycanthropes, and undead do battle with demons and their demon lord masters while ancient dragons, mindflayer colonies, and corrupted constructs carve out territories of their own. Anything evil and vile can be found in Accorion, either trying to escape or fighting for control. And, alongside those evils, other entities -- good or bad -- who would see them destroyed wrest control of footholds and bastions to wage war on Accorion's prisoners.

Travel

Reaching Accorion can be done with the usual planar magics or Ipacian travel; sadly, since its shattering, there have even been rifts appearing across Yophas in those places already weakened to planar tampering or wild magics, though those portals are often shifting and ephemeral. The region of Ipacia surrounding the Halls of Black is choked with debris from the plane's shattering, which can pose troublesome for obvious reasons, but because of the realm's broken state, its borders with the Realm of Stars have been torn. This means that, in theory, Ipacian sailors and travelers can actually pass between the different portions of the plane and head "directly" where they might want to. In practice, the devastation of planar laws means that traveling between portions of Accorion can lead to unimaginable consequences, such as randomly colliding into or entering pocket planes that weren't there a second ago or being attacked by ravenous aberrations. Travel within Accorion can be just as chaotic and is even more dangerous, doubly so in more active portions of the plane.

Type

Dimensional plane