Classes

Arcane classes (artificer, bard, sorceror, swordmage, warlock, wizard)
•The artificer is not playable in Dark Sun. A class that accumulates potions and magic items doesn’t work in Athas, where most magic items are rare.
•The swordmage, however, IS playable.
•All arcane classes have the ability to defile — when rolling an attack roll or damage roll for an arcane daily power, a character can choose to reroll, taking the second result, although this deals necrotic damage to all of the target’s allies within 20 squares, equal to half each character’s healing surge value. This damage cannot be reduced or prevented in any way.
•In Athas, all arcane classes (yes, even bard) have a reputation as defilers who suck the life out of the world and as heartless marauders who would do anything in pursuit of power. Thus, almost everybody will react with hostility and violence on using arcane powers in public. The only spellcasters who are able to get away with it are templars, because they receive special dispensation by the sorceror-kings. While part of the negative reputation for arcane spellcasters comes from the sorceror-kings wanting to get pre-emptively rid of any competition, the majority of arcane spellcasters do actually succumb to the lure of defiling.
•The warlock’s pacts are slightly retooled for consistency with the campaign world: the fey pact taps into power from the dying Lands Within the Wind and its surviving eladrin princes; the infernal pact draws power from fiends trapped in the Gray, looking for a way to enter Athas to wreak havoc; the star pact derives power from abominations said to live on Ral and Guthay, Athas’ two moons; the dark pact takes power from the Gray’s power over death and shadow; and the vestige pact draws upon the civic traditions of Balic, embodying the stalwart historical figures of noble virtue.

Divine classes (avenger, cleric, invoker, paladin, runepriest)
•Divine classes are not playable in Dark Sun, as the gods are all dead or unreachable.
•However, the warpriest (the Essentials version of the cleric) IS playable, reflavored as a primal class (because the domains for that class are all sufficiently element-themed).

Martial classes (fighter, ranger, rogue, warlord)
•All martial classes are playable. Indeed, in as harsh a world as Athas, everybody alive knows how to defend themselves.

Primal classes (barbarian, druid, seeker, shaman, warden)
•All primal classes are playable.
•In the wastes and the villages, wielders of primal power act as healers and defenders for their villages or tribes, making it quite widespread.
•In the cities, the sorceror-kings have put forth propaganda for centuries that primal power is derived from enslaving natural spirits and not to be trusted, and as such, templars keep a stern eye on primal characters.

Psionic classes (ardent, battlemind, monk, psion)
•All psionic classes are playable. In fact, in Athas, every living being has some amount of latent psionic power. Most manifest as wild talents, but psionic training academies (where it is called The Way) are very common in every city. Psionic abilities are very common, and nobody looks twice at anyone who manifests them in public. Most arcane spellcasters do their best to disguise their spells as psionic powers.

Shadow classes (assassin)
•The assassin is playable. Its shadow powers are derived from the Gray, the shadowy realm that acts as a barrier between Athas and realms beyond.
•The vampire is NOT playable, as they would have a big problem with direct sunlight in a world that averages 130 degrees by noon. Vampires might still exist — there are some places they could reasonably stalk prey undetected — but they wouldn’t be mobile enough to be playable characters.

Classes

Midnight at the Oasis BentonSancho