1) I have players who want to be: a Wilden, a Shifter, a Changeling, and a Githyanki. How do/could all of these races fit into DS? I'm willing to be flexible, but I'd like things to have as much internal consistency as possible.
2) There are no dragons (except THE Dragon), right? Were there ever any dragons (e.g., in the Green Age)? I've got a player who wants to be a dragon (polymorphed involuntarily into a human, natch), and I'm having trouble making it work in my head.
Keep in mind, I don't want to say 'No' if I don't see a really striking reason to.
2. No dragons that I recall. It's been a while since I looked closely to all the history. What is he looking for in the character? Can he change back? Is he in human form permanently? Sounds a little powergamey. If he has been changed permanently to human form then play a human. Or, if he is to retain some dragon aspects, play a dragonborn that looks like a human. Mechanically he uses the dragonborn stats but he just looks like a human.
What books are the tigones or tagsters in? I've got a friend with a few of the older DS books, so I might be able to look them up.
The Wilden is more problematic... I'd rather it be a race than just a one-off character, as I don't want to deal with a player having the only walking tree in existence, and the attention that would bring. Is there a suitable location that a few Wilden may have originated? Maybe one of the two wooded cities? Then I can have more of them exist, and the character will be more of a curiousity than an aberration.
About the dragon... it's definitely more of a roleplaying thing than a power-gaming thing; the player just really likes dragons, and wants her character to believe that she is one, trapped in human form. I was just having a lot of trouble justifying anyone even knowing the concept of a dragon if there's only one out there.
1) She could be the "unwanted" child of an Sorcerer-King or another athasian Dragon (like Graytch or Farcluum), that would make her kind of a Half-Dragon.
2) In the past, an Psionicist damaged her mind irreparably, since then she believes to be a Dragon, though the Player thinks he was one, the DM knows it's all in her head.
3) The elemental Drakes were once intelligent, maybe she is an outcast who was punished and changed into an human being or genasi. (People often mistake elemental Dragons to be the real athasian Dragon, Borys)
1) She could be the "unwanted" child of an Sorcerer-King or another athasian Dragon (like Graytch or Farcluum), that would make her kind of a Half-Dragon.
Perhaps her mother is one of Nibenay's shadow wives, and she's convinced that Nibenay himself is her father? She might even be right.
About the Dragon:
I really like Masato's comments. I had some similar ideas. I commonly refer to "Dragon" on Dark Sun as a title, rather than a creature. For example, it can be used interchageably with "Archmage" or "Sorcerer-General". The Dragon of Tyr is the most powerful Mage that gained the power to turn into a Dragon (rather than the other way around). Usually Dragons are Defilers, however, most average people cannot distinguish between Defilers and Preservers. Thusly, "Dragon" could refer to a powerful Preserver instead. The player might have a been a powerful "Dragon" (ie powerful Defiler/Preserver Arcane User)... and maybe their mind was wiped (Masato's post #2) or died and was reborn as a Deva.
If the PC really likes Dragons as a creature, use Masato's Elemental Drake idea. Drakes were 'once' (in myths and legends) intelligent. What happened? Where did they go? Why are they now unintelligent, savage brutes? Does it have to do with Defiling?
About the Gith[yanki/zerai]:
These are all very planescape-y race. But they could work in a setting that offers lots of Psionics.
Option 1) The Gith are a deformed race. There is speculation that they are decendants from Githzerai or Githyanki, but there's only one adventure and the adventure is very planescape-y. Gith are very Dark Sun-y and very intelligent, and I'd recommend looking up their race fluff. For stats, you could use Githyanki. They make excellent Wilders or Wilderness nomads. Gith are also sometimes employed as scouts, mercenaries or psions. However, Gith tribes are often hostile to travellers and merchants, and NPC reactions should be similar to those of Orcs or Gnolls on other worlds.
Option 2) The Githzerai would work wonderfully on Dark Sun, IMO. Their hidden and recluse monasteries train psionic and martial class characters. Githzerai use the harsh terrain and world as a training ground. Githzerai would work very hard to keep the location (and any other information) of their monastery secret... even going so far as taking the secret to their graves. Githzerai characters might have some interesting conflicts with the Order (against or for). Monasteries send a single (PC/monk) outside to accomplish a very specific mission - something very important, and the PC might not even know what it is until later.
Option 3) Githyanki. I don't have the foggiest clue how to adapt the fluff of the Githyanki from FR or Planescape in Dark Sun. The Githyanki could be trying to infiltrate cities to find the Githzerai? They could be strangers from another place. They could even be from a militant monastery like the Githzerai above.
About the Wilden:
Making them a "general" race will be difficult unless they're from Gulg. In that case, they could be a Templar of the Oba (on a mission)? It could work, but everybody would be able to distinguish her as Gulgan. Otherwise, you can use both the Crescent Forest or Forest Ridge as having "populations" of Wilden, that have risen by Primal Spirits.
Otherwise, Wilden can arise from the desert. They'd look more like cacti or shrubs than trees. However, having desert/sand Wilden tribes, nomidic tribes of course, would work well (lost, constantly searching for their dead forests). Maybe they like the wastes and hate cities. Elves could trade between the nomadic desert Wilden, Eladrin and cities. Wilden, of course, would hate Eladrin.
Note: the seasons of Athas are Hot, Hotter, Hottest, and Baking. I might adapt the "Seasons" of the Wilden to represent different types of desert heat. Work with your player in that.
If the campaign takes place in Tyr or in the Wastes, ignore me.
...just saying.
Thanks for the help, everyone.
Karak's death finally broke the shackles of despair from the primal spirit of the land, and Wildens are its agents, the 'strikebacks' of Athas. Now, the land has known hope once again.
Thanks for the suggestions, though.