The trait a pokemon gets is random. So if you're breeding Manectrics, the offsprings with have either the static or lightningrod abilities. There is no way to guarantee that the hatched Electrike will have static, it's just random.
And if you keep breeding, you should eventually hatch an offspring with hp grass. It could take a while, though, since IVs are random, and there's sixteen different types hidden power can be. (Since it can't be normal) So, just keep on hatching a lot of eggs, and test the hidden power of each Electrike until one has hp grass.
That's all you have to do, hatch a LOT of eggs.
EDIT: Got beaten to it, lol.