So long as you don't put magnezone up against its weakness (fighting, ground & fire), magnezone is pretty good and I wouldn't recommend benching it. As for moves you can take out mirror shot if have flash canon as well as spark. But Ame doesn't give that many TMs so there's not that many noves to replace it with. So I would recommend replacing mirror shot with a moves like barrier and light screen (them strategies), you can also replace it with mirror coat if you want (though it's kinda gimmicky). As for spark, replace it with Volt Switch (if the TM is in the game, I'm not sure) or a stronger electric move like thunder. You would wanna keep Flash Canon (solid Steel type move) and Discharge (Aoe plus chance of paralysis) and if you go double battle with it you can use Flygon or Swampert so they wouldn't get hit by Discharge.