wotc said:The most well known demiplane is Sigil, City of Doors. No one knows who created it or how, but Sigil holds portals uncounted that lead to every other plane of existence. Veteran planar explorers soon learn that Sigil is the first place to look when a door to somewhere else is needed.
I imagine there will be certain Rituals, PPs, Feats, whatever that can trigger it. This is simply the base formula and the Skill-used will be stated in the Ritual for instance information.The problem with the Unstable PLane skill thingie: it doesn't specify what skill to use. If it's literally "Any skill applies", then I'll just use Acrobatics to moon-walk the land apart. (Honestly, the idea of using Bluff/Diplomacy/Intimidate/Thievery to alter the terrain would generate some really interesting, and epic, explanations. I can see a thief creating a portal by "Pickpocketing" the dimension).
I would consider myself a Planescape fan... Well more a Sigil fanVery interesting. I wonder how the Planescape fans will feel about Sigil being a demi-plane, and it's relationship with the other planes.

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