so, Dark Sun is indeed
different, which is good!
ok let's look at it:
4th ed does have rules for environment threats DMG Page 159 and under Endurance and Nature skill in PHB
anyway, it should be easy to have more rules for that due to Dark Sun's climatic and environemnt extremes, as it's a Skill Challenge.
Fail = lose 1/healing surge/per 8 hours, or special event.
Which is a much nicer mechanic than prior verisons of D&D, IMHO

(though 3rd had skill system that was a heck of a lot better mechanically than 1st/2nd, it got tad complex)
Deva's do make sense..spirits of the ancient people's re-born again anad again wanting revenge on the Sorceror kings!
The rest..as I've said elsewhere, I had an epiphany about Dark Sun:
mutations!
It's a world where the environment, magic and the Dark Sun itself triggers mutations (and in the official history the Pristine Tower directly creates mutations in anything wandering by it)
So, pal wanted to play a goliath, and I thought,
hm, why the hell not?
the character looks human, but isn't (though he has human Size so can't use larger weapons). back story is he was changed by encountering anncient spirits of priests burning with revenge...so now he's an Aveneger with race "goliath" though he looks Human.
Works for me!!!
