Anteris

Anteris is a rarity among the planes in that it seems unanchored. All planes drift in the Mist to one extent or another. Normally, this is a glacial, geological process. Portals, as practiced by mages, only connect two worlds that are in fairly close proximity. Generally speaking, planar locations can be treated as static by even long-lived mages. The worlds are where they are and they move at a slow pace over milliennia. Anteris is an exception. It phases in and out of the Mist relative to other planes on very short notice. Sometimes less than a week. The inhabitants, if they're aware of this at all, haven't shown any negative effects from it. Planar cartographers bang their heads against maps every time it moves, which it does on unpredictable time tables to unpredictable locations.

Anteris is one of the older Primes that exists. It's impossible to determine exactly how old. Time passes there at the same rate as (almost) all the other worlds, but the plane itself moves around in time as well as metaspace. It's existed long enough to have a stable portal open in Nexus, one that usually works but goes cold while Anteris is transitioning to a new place. Despite the reasonable availability of the plane from Nexus, it doesn't see a brisk trade from outlanders and this perhaps because the Nexus portal opens into very dangerous territory. The only stable route into Anteris is on the west coast, guarded by very large cannons and manned with very poor senses of humor. That fact may also account for Anteris's relative obscurity and its total lack of attention from dangerous metaplanar powers.

The few natives that do take up an extraplanar adventuring career boast that their world invented firearms, perfected them, and perfected sharpshooting with them. The veracity of this is impossible to verify, but no one argues that Anteris firearms are peerless and very few argue that they are more skilled pistoleers than Anteran Gunslingers.