Interesting. Well, for the water-electric type, I think a siphonophore could be interesting. Siphonophores are basically a bunch of tiny creatures combined into one. Perhaps a creature based on the Portuguese Man o' War or that one 50 m-long siphonophore could make a pretty cool legendary, considering how excessive and OP the universe let these things get.
The steel/electric type gets a little tough because I want it to fit with the other two and possibly be aquatic. The other two, though, are a bit more natural, and such typing used mostly for inanimate, modern-type objects just make all my ideas feel like they'd be too standalone and out there. However, I do have one idea that may work.
Hammerhead worms are highly invasive creatures and are more or less impossible to kill. Cutting one up will make all the pieces regrow into their own worm. Perhaps a legendary Pokemon of this type based on one could be made up of several tiny magnets that make cutting it up to kill it a futile effort. Maybe it could be a much more destructive Pokemon similar to its real-world counterpart.
Caption this Meme
