My Golduck knows the move Soak. I'm not sure if you are familiar with it, but it normally changes an opponent's type to water.

Of course, it's hard to say how effective it will be on a creature like this. but if we could change its type, even if it is just for a while, we could probably really do some damage to it. And with electric attacks, we wouldn't need to get close to it. And it might even end up paralysed which would be a great help.