My mentor Alexis Smolensk, of The Tao of D&D, has created a marvelous system of knowledge skills for his world, through which player characters slowly gain abilities which improve their understaning of the game world, and their ability to create within the world. I use his system for my game, and the players like it very much; you can read more about it here.
Velue, the illusionist in my ongoing campaign, has chosen the study of Planar Gating and Travel as his first area of expertise. As Alexis has not yet written up his ideas for that study, I took some time tonight to write up a rough plan for the abilities Velue will obtain. These four tiers are unlocked at certain thresholds of points within the study; Velue currently has access to the Amateur abilities, and may gain the Authority ones as soon as 3rd level, if he's extremely lucky (points are gained by die roll.)
"Planar Gating and Travel provides knowledge of how to transition self and others from one existence to another, granting the wherewithal to cross into the ethereal or across the astral planes." (A. S.)
Amateur
- Recognize Extraplanar Manifestation: know the typical stats and plane of origin for extraplanar creatures and phenomena, and recognize the same when they appear on the Prime Material.
- Understand Planes: knowledge of the terrain, features, hazards, and native entities of the other planes.
- Determine Destination Plane: tell which plane a portal leads to.
Authority
- Contact Other Plane
- Ethereal Jaunt: shift oneself into the Ethereal Plane, allowing one to bypass many Material obstacles.
- Extraplanar Mentalities: understand the motivations and behavior of extraplanar creatures, which also grants increased ability to bargain with them.
- Determine Precise Destination: tell exactly where on a plane a traveler will end up if they pass through a portal.
Expert
- Astral Projection: send spirit through the Astral Plane, temporarily creating an effect similar to the Avatar spell, but capable of reaching any plane.
- Call Extraplanar Denizen: summons a typical inhabitant of another plane of existence (not including those planes which are "religious" in nature, such as Heaven, Hell, Nirvana, Olympus, and Asgard.)
- Create Planar Exclave: link a tiny region of the Prime Material with another plane, transforming the region to resemble that plane.
- Construct Temporary Portal: build a magical edifice which manifests a one-use portal to another plane.
Sage
- Construct Permanent Portal: as Temporary Portal, but the edifice will automatically become reusable after a period of time (alternatively, it stays open during specific periods, such as a phase of the moon, but is totally closed at other times.) Edifice will resist destruction by mundane means.
- Acquire Planar Characteristics: permanently acquire characteristic feature of creatures native to another plane.
- Create Pocket Dimension: warp space to create a personal retreat outside of reality itself.