I forgot about Yerth because I added my own Ierth (which would be pronounced about the same). I suppose they're different worlds, but due to the similarity in name, the arch-mages think they are the sameWhat? No Yerth?

I forgot about Yerth because I added my own Ierth (which would be pronounced about the same). I suppose they're different worlds, but due to the similarity in name, the arch-mages think they are the sameWhat? No Yerth?

Yes. I first came to fantasy through Moorcock and so in my mind all settings are part of the multiverse for me, stated or not. This happens often in my mind and my campaigns where resonances, echoes, memes, NPCs and even PCs slip and pop between settings, all and any of them.
That's how I have always viewed fantasy and I extend that to all genres and settings.
However, that's me. As a player I respect the GM and their visions.
Posted by C4-D4RS on the MetroLiberal HoloNet
I never cared for Planescape; though the art was wonderful and it had some interesting ideas, it always rang as a "gritty reboot" of Spelljammer to me. To my mind, what defines a setting is as much what's NOT there as what IS.
Currently, I run a Primeval Thule campaign, and by necessity my multiverse does not contain high fantasy worlds or elements. As described in the Primeval Thule Campaign Setting, other worlds exist, but serve as a source, not a destination. You can summon a great and terrible genie or demon or fairies or whatever, but you aren't going to visit them at home. Thule defines these planes as parallel dimensions and alternate Earths and I like that idea.
Now, the concept is structured such that you could choose to interpret everything as being part of the Great Wheel or World Axis or wherever you want; after all, just like the people of Krynn coloquially refer to the Nine Hells as the Abyss, the difference between the Parallel Earth That is Made Of Flame and the Plane of Elemental Fire is largely academic. But I like working with constraints, and so I chose a more literal interpretation.
TL, DR; no, my campaign setting is distinct from and does not interact with the D&D multiverse.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.