Politoed

Politoed here isn't building toward a dedicated Rain sweep, since there's no Swift Swim user, no Mega Swampert, and no Archaludon on the team. Its real value is making opposing Mega Charizard's life much harder, since Heat Wave and Solar Beam hit for far less in Rain than in Sun. Icy Wind provides speed control for the rest of the team, and Calm with max HP and Defense keeps it durable enough to keep providing that support across a long game.