>>22222121I've said it before, and I'll keep saying it until it happens:
I want the next region to have some kind of abandoned/burned out nuclear power plant or lab that was researching nuclear energy, and in this place there are a duo of unique pokemon that only exist there that are Poison/Fire and Poison/Electric and are based on toxic radiation. Extra points if they have a complimentary ability that boosts each other when they're used together (Fission/Fusion maybe?) or has some other beneficial effect, like regenerating each other when they pair up. Extra extra points if they each have a signature dual-type move like Flying Press that has a chance of inflicting badly poisoned or burn/paralyze respectively. They'd make a badass addition to the roster of "scientist" trainers.
Poison/Steel would be a cool one as well if they wanted to make it a trio of "Nuclear experiment gone wrong" pokemon, but Fire and Electric just lend themselves more to the idea.