>>18419880I believe that M.Blastoise works best in the singles department. While Mega Launcher is a nice ability, the main selling point is the increase in stats that Blastoise gets. A solid build for Blastoise's case is 252 HP/252 SpA, allowing it to hit hard and take hard hits.
For move sets, you'll want to have Aura Sphere and Dark Pulse in those sets. For myself, I use Dark Pulse/Dragon Pulse/Aura Sphere/Auqa Jet. Now the question you are probably asking is "why the hell Auqa Jet?" Well, with Blastoise's increased stats come an increase to Attack. With that in mind, running Aqua Jet comes as a surprise to most players expecting Water Pulse when the opponents poke is something like M.Tyranitar or Aegislash.
Good partners would be any poke with respectable defenses and resistance to Electric and Grass attacks and the occasional Dry Freeze. Good partners would be Dragon types and Steel types. In my case I use Goodra and Metagross with Goodra being Max HP/Max Def stall build and Metagross being Max HP/Max Atk agressive with either Lum Berry or Assault Vest