Tyranitar is pretty important, actually very important since it helps you counter so many threats to your team. And you can also use Rotom-W in place for Magnezone. Here's the set:
Rotom @ Leftovers -- Levitate
Nature: Modest - EVs: 252 HP / 252 SAtk / 4 Def
Hydro Pump
Thunderbolt
Pain Split
Will-O-Wisp