So, the concept is that the world came to an end. While I'm still not too certain how, a part of me is leaning toward the idea of a magical cold war that resulted in everybody "nuking" everybody. Years later a group of mad scientists arose and used magic, science and technology to sort of revive civilization in the wastes. The newly established test cities (whether these are experimental cities or cities where the scientists experiment on the citizens is still uncertain) and are powered by slime, a magical byproduct excreted from oozes, essentially imagine pipes carrying neon colored fluid and that serve like powerlines, attached to every building and outlet.

Note: I don't own any of these images, I am simply using them to convey my thoughts.

The idea is that these mad scientists, the Council of Geniuses, as they call themselves are kind of like the founding fathers of this new world, their legacy affecting the world decades/centuries later. While I haven't come up with names for them, I do have a general idea of the different "studies" that they focused on:

• Necromancy/Lightning - Kind of like Frankenstein and his monster. Necromancy is a common and accepted practice in this world (so hooray for players who want to play as necromancers and not be hunted by the inquisition every five minutes ).
• Slime and Constructs - Slime is the main power source in this world.
• Mutations - Harvesting genes from an ancient, mutated creature called the Homunculoid, they can genetically mutate humanoids for practical or cosmetic use. Secretly this scientist is also responsible for the establishment of vampirism and blood magic (both of which are looked upon with suspicion and disdain).
• Transhumanism - The desire to evolve humans beyond the boundaries of the flesh into the mechanical and beyond. Perhaps even living weapons/armor (kind of like Ripout).
• Celestial/Psionics - The study of both the stars as well as psychic powers. One thought I did have was that in this setting they might use portals to explore/raid other worlds and bring back resources. Not one hundred percent sure about that.

Would like to explore how society grew out of these various mad experiments with different cultures and even religions taking influence from these experiments. Like there could be an order that practices both lightning magic and necromancy, viewing it as a means of praising/worshiping their scientist that they worship.

So aside from humans most other player races are the results of genetic/magical experimentation. Elves for example were once pompous noble humans that just wanted some traits to "prove" their regality to those they deemed "inferior." Of course, nothing goes as expected when dealing with crazy scientists/mages.

Plasmoids are playable sentient oozes. Might also try to add a monkey and rat races as both are creatures that have been experimented on in human history to a great extent.

I am considering making some racial feats for some of these races (seeing as WotC chickened out of creating racial feats after Xanathar's Guide to Everything for some reason). Maybe give vampires (dhamphirs) some bloodline feats, plasmoids could have their unarmed strikes deal acid instead of bludgeoning damage, perhaps changelings could develop the ability to absorb weapons, which they can conceal inside their body and pull out at a moment's notice.

While outside of the cities, you are free from the influence of the mad scientists, you reside in a largely ashen/ruined wasteland with horrific monsters wandering around. Many of the monsters that the players would come across are the result of corrupted/mutated creatures from before the magical fallout as well as discarded experiments from the mad scientists. There might even be mutated kaiju like monsters outside of the test cities, kept at bay by some sort of invisible, magical barrier. Also, possibly angel/alien creatures, who maybe secretly influenced the destruction of the former world.

The wastes seem to come alive when the sun goes down. Some of the plants have glowing leaves, sap and fruit, as well as some of the monsters which will try to use their lights to lure in prey.

Sometimes people are hired to go out into the wastelands either to scavenge resources, dispose of unwanted property and trash (or potentially failed experiments), or the investigate strange anomalies. One type of anomaly are spectral forms and images of things that happened before the world came to an end.

Might try to mix of some tropical elements too. Like how many post-apocalyptic settings take place on an island or on a tropical coast? Might try to borrow some elements for Hawaiian/Polynesian culture (I just think their culture is pretty cool ).

I'm kind of leaning toward a modern/steampunk aesthetic but using magic, slime and other crazy things to make a potentially wacky and fun setting. Perhaps most of the store vendors could be constructs/vending machines.

But please tell me what you think and feel free to offer ideas/suggestions either for how the setting works or even characters that might be fun to see in such a world for a DnD 5e game.

I like it. Not sure what advice I could give though.

7926111 Well, any ideas could be useful. Even some atmospheric music that you think fits the setting might be helpful.

7925808
Makes me think of that one planet where Jimmy Neutron and the kids of Retrville went to save their parents.

7926559 It has been quite a while since I've seen that movie.