Geron Raveneye
Explorer
Everybody has slightly different sacred cows...interestingly, the Elemental Planes as they are right now are one for me, simply because they appear in nearly every incarnation (and most campaign settings) of D&D. The Outer Planes have looked differently from time to time, but the Big 4 were always there. They always were something of the building blocks of the Prime. I actually added the Positive and Negative Planes to Mystaran cosmology because I liked the arrangement better. Everything else can go through as many changes as they like...in the end, most DMs will create their preferred cosmology anyway, and adapt the monster stats as good as they can. But tinkering with the Elemental Planes kinda tinkers with the building blocks for the Prime.
All IMHO, of course.

All IMHO, of course.
