The lowest layer of Acheron, and by far the most frigid and deadly, Ocanthus is nearly as close to uninhabitable as an environment can get: temperatures far below freezing, constant biting winds, the air filled with flying shards of vorpal-sharp black Styx ice. Nearly as empty as Thuldanin, there is only one city of any note in Ocanthus, though it's an especially significant one: Zoronor, the City of Blades, home of and refuge for the bladelings. The mouth of the river Styx, it is this layer where even memories no longer survive; where war and conflict have faded so long into the past that none can even speak to them anymore, that even history itself is unable to record anything of long-dead struggles.
It is only in Ocanthus that temperatures fall low enough for the churning waters of the Styx to freeze, solidifying as they fall from Tintibulus into wide, razor-thin black disks drifting on the winds of Ocanthus, each with its own individual gravity as the cubes above. As in all layers, these disks drift about the layer and at times crash into one another, though here they shatter immediately on impact into the layer's signature shards — or "dark birds" as they're commonly known, a calque from the bladeling tongue. These shards fly about, slicing through nearly anything in their path without slowing down, but they eventually shatter as well once finding a tough-enough obstacle (or colliding into one another). Here, though, the dust of their remains does not merely float free, but rather settles down upon the endless midnight-black sheet of Styx ice at what seems to be the lowest portion of the layer, adding to its thickness incrementally. What the sheet rests upon (if anything) is unknown, as is its depth. However, it's believed by many that all memories taken by the Styx eventually settle here given enough time, and can still be found somewhere within the river's finality.
For obvious reasons, few bother to visit this layer, and as such little is known of its details. All visitors tend to keep to the sheet-ice, as the disks themselves are too fragile to support much weight, and in the air one is at much greater risk from the shards. Zoronor is located upon the sheet, as is the Cabal Macabre, the center of Wee Jas's realm. Further, in "distant" sections of the ice, one can find the occasional well-warded modron mining colony. Here, at least, their existence is somewhat more sensible than on Tintibulus, but it's still a commonly-debated question just what memories modrons might be looking to uncover.
Each round a person or object spends on Ocanthus, it has a chance to be struck by a shard of Styx ice. Treat this as an attack roll with a +10 modifier; on a hit, the target takes 2d6 damage. This attack penetrates damage resistance, but hardness still applies. On a critical hit the target does not take any additional damage, but takes a -1 penalty to Intelligence for as many rounds as damage dealt due to the effects of Styx water, slightly blunted in its solid form. This penalty stacks, but upon reaching 0 Intelligence the target falls unconscious rather than dying.
- Manual of the Planes (3e), pp.126-127
- Planes of Law - Acheron, pp.24-25
- Planescape: Torment