Well, it's one of the most favorite pkm to me. Btw, I would like to leave here some possible suggestion too.
Truly, spikes has been a kinda of annoying and sometimes unless moveset. Basically it causes a seriously low damage (sometimes it not even does) and works more as trap, causing too much bothering.
So, my suggestion would be for you replace spikes by tectonic dance (i know many may say nidking has it in its tmset, but c'mon that's one from those new tms, surely so less people has added it to nidoking, and an extraction wouldn't affect in anything. Even though, it has benn so tough to find tm tectonic dance).
Magnetude, well, i can't see nidoking becoming opness keepin' it plus tectonic dance, although it may be, you could replace it by earth power. what would be an interesting thing too.
Mud, replace it by rock slide, it for sure would give a little of differential to nidoking.
and for finish, dunno if it would ask too much, but put rage back as passive, would help it a lot too.