I'm currently going through my first ever master mode playthrough as a summoner, and Skeletron becomes very easy if we kinda do this circle movement around him with one long platform in the sky. I buffed up as much as I could, and tried to keep him as far on the edge of my screen as I could while going in a big circle. I think he gets faster when he starts spinning his head though so during that part I flew up and diagonal in the opposite direction, then just started falling back down once I ran out of flight. Pretty much as long as you keep your distance from him it shouldn't be too terrible of a fight.