Future Eberron - Post apoc world

[Andor]

That's a good question: why are humanoids immune to poison?

1000 years of surviving off of toadstools, wild almonds, and fugu?

 

[Werebat]

In eberron's history, there have been multiple cataclysmic events ending various ages.

This. You could easily run a post-apocalyptic world set in the time of the Daelkyr invasion of Khorvaire that ended the Age of Monsters. Players could play Bugbears, Hobgoblins, and Goblins (and of course Orcs and maybe some of the at-the-time obscure native races like Dwarves and Halflings as well), either struggling to beat back the Daelkyr that have shattered their civilization or trying to survive in the ruins just after the Daelkyr are locked away.

There'd be lots of recent ruins, lots of mutated aberrations, maybe even some lingering "radioactive" areas tainted by the essence of Xoriat.

 

[Werebat]

...you could go with plain old "mundane" radiation. In a magic-driven society, normal radiation would probably be really, really strange, because dispel magic and so on doesn't work, nor would it care for magic (like Wild Magic and stuff) - for a magic-driven society, that's pretty unfathomable.

Cheers, LT.

I tried to use real-world radiation (as much as possible) in a 2nd Edition game once, years ago. It went wonky pretty fast as a character went into gaseous form and then floated into a highly radioactive area. I had no idea how to handle that given what I knew about the different types of radiation they would be encountering, and the fact that they were gaseous meant (among other things) that they had no skin.

Real world radiation isn't actually a lot of fun to even try to emulate, IME. Even Fallout doesn't really try that hard. You're best off coming up with some magical alternative.

As for radiation being "immune" to magic, either it has some inherent antimagic properties (which doesn't make a lot of sense because LIGHT is clearly affected by magic and is itself a form of radiation), or it wouldn't take long for enterprising magic users to create "Protection from Radiation" spells (for example).