D&D General Baldurs Gate, Darksun, Fallout Mashup.

[Argyle King]

Well underdark is a thing in D&D so vaults kinda obsolete.

That's a good point.

Still, Vaults could be Dwarven communities which chose to isolate themselves. They could be one part Fallout and one part Dragon Age Dwarves.

 

[Zardnaar]

Lizardfolk (or perhaps Kobolds given the general culture and vibe of desert lizardfolk) would fit a post-apocalyptic world. It may be interesting to see how they interact with Deathclaws.

I was trying to think of how to do ghouls, but I'm unsure what fits. Both Dhamphir and Reborn kinda fit but also kinda don't.

For a second choice, I have a few thoughts, but I don't think they fit the vibe you have in mind. I had been thinking either Plasmoids or Tortles, but that's less because of your idea and more because I feel those would fit well with the three species you've already highlighted.

I'd keep Dwarves, as they could easily work as a version of isolationist vault-dwellers.

I might remove Dragonborn as a player race. Instead, they become the elite shock troopers, city guards, or whatever else is needed by the Sorcerer Kings.

If you use kobolds as little lizardfolk, I would cut one of the usual PHB shortfolk.

Ogres could work as Super Mutants, with Ettins and Hill Giants being special versions.

Well Gnomes woukd be number 1 to cut I can tweak the fluff on halflings.

Your Dragonborn ideas not bad servants of the Sorcerer Kings.

 

[LuisCarlos17f]

My suggestion is recycling elements from Gamma World, and borrowing lore from Mutant Year Zero.

Illithids are one of the iconic monsters of D&D brand, but there are also other sentient aberrations, for example the zerns(3.5 MMIV) or the kaorti and ethergaunts(Fiend Folio), or the tsochars (Lords of Madness: Book of Aberrations).

The cult of Thoon from MMV could be interesting, but I would add some powers working like incarnum soulmelds.

Shardminds could have been humans who survived a "grey gloo" infection.

Other idea is the living constructs are allowed for the players, but there is something like an elemental red red weed plague, and then the constructs need "food" and water for healing and stop the infection.

 

[Zardnaar]

My suggestion is recycling elements from Gamma World, and borrowing lore from Mutant Year Zero.

Illithids are one of the iconic monsters of D&D brand, but there are also other sentient aberrations, for example the zerns(3.5 MMIV) or the kaorti and ethergaunts(Fiend Folio), or the tsochars (Lords of Madness: Book of Aberrations).

The cult of Thoon from MMV could be interesting, but I would add some powers working like incarnum soulmelds.

Shardminds could have been humans who survived a "grey gloo" infection.

Other idea is the living constructs are allowed for the players, but there is something like an elemental red red weed plague, and then the constructs need "food" and water for healing and stop the infection.

I have been reading lords of madness