Venusaur

When Mega-Evolved, Mega Venusaur has the ability Thick Fat, which neuters Fire- and Ice-type moves, making it only weak to Flying-, Psychic-, and Teravolt Ice-type attacks. The combination of Thick Fat and its increased stats makes Mega Venusaur a fantastic tank, especially against rain teams, and as a win condition, meaning it's great at winning the game if you remove its checks. Alternatively, non-Mega Venusaur takes advantage of the ability Chlorophyll and its base 80 Speed to outspeed virtually anything when the sun is up. Venusaur has a great movepool with access to powerful STAB attacks as well as the useful support move Sleep Powder. Its non-Mega Chlorophyll set takes advantage of its high Speed to deal good damage and spread sleep, and it has strong offensive synergy with Mega Charizard Y. However, both formes are weak to common Fire- and Psychic-type threats, such as Talonflame and Cresselia, and are also reliant on Sleep Powder and Leech Seed to do anything against Steel-types.