I don't think Mc's problem with eletricity has something to do with the material he is made of, actually i think it has to do with how the energy interacts with his inner monster energy, i have the impression that eletricity powers his abilities whitout control expanding his flesh, so changing himself to rubber for example wouldn't help.
I agree with that, but logically, if the energy can't get into his body, then it can't hurt him.
I'm not talking about something like a rubber body here, but a protective layer on the surface of the body, made from a material that would COMPLETELY ignore electrical energy. From what we've seen in the game so far, his problem with electricity is that it prevents him from changing form and reverts him back to his black slime form. The key is to create a layer that simply doesn't allow electricity to get in so it can't cause a chain reaction. But for the MC, such a thing is highly difficult, since all his transformations have a biological basis.
My guess is that the understanding and use of different kinds of monster energy is related to the use of memory, not body, so Mc would have the advantage on that.
Energy is simply energy.
In the case of monsters, how you shape it depends on your body, innate talents and skills.
MC can mimic a faucet, but cannot mimic the type of water that will flow from it.
I think Ella should fundamentally have a much better understanding of that energy (if nothing else).
Like I said, this is just my guess, but if anyone could mimic some of the powers, Ella is best suited to do so.
However, I am only talking about purely physical passive abilities.
I certainly don't expect her to be able to copy things like teleportation, mind reading, or throwing fireballs.
Also, I think the energy that monsters use to enhance their weapons, skin, strength, and speed is just some kind of universal energy that doesn't require a specific focus. It should definitely be the easiest power to imitate.