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Hey,
First off thats a really good sketch. Next your team appears to be weak to opposing sun teams. Opposing Volcarona can be a real pain for your team to face and Specially Defensive Heatran walls your 3 offensive mon's. Its a real pain if its got Air Balloon to evade your Dugtrio and Wobbufett is going to be crippled by a Toxic if it comes in. Also noted was Mamoswine can be really annoying for your team, but it can also helo you patch up a lot of issues. I'm not sure what to replace but I think putting in a Life Orb Mamoswine over either Volcarona,Starmie or Venusaur could help you tonnes. It helps you by giving you a reliable Priority move in Ice Shard which can help you against the troublesome Theirans, and its Superpower and Earthquake can help you defeat annoying Tentacruel and other special walls like Blissey and Chansey.
GL with your team, Mamoswine set below