Venusaur

Mega Venusaur has a solid defensive typing with adequate bulk and Thick Fat, which leaves it weak to just Flying and Psychic. This also means it is the only viable Grass-type that is not weak to either Fire- or Ice-type moves, giving it better matchups against Mega Charizard X and Choice Specs Greninja at the same time, one of which other Grass-types like Ferrothorn and Whimsicott may struggle with. It is one of the bulkiest and least passive Leech Seed users, with powerful STAB and coverage moves in Sludge Bomb, Giga Drain, and Hidden Power Fire to help it break foes like Greninja and Tapu Bulu, as well as Taunt users like Mega Mawile and other SubSeed users like Serperior and Jumpluff. It also has access to reliable recovery and stat-lowering moves via Synthesis, Rest, Sleep Powder, Charm, and Amnesia to beat offensive threats like Mega Charizard X. However, Mega Venusaur has no viable way of boosting its offenses, so it is susceptible to bulkier Pokemon like Type: Null. Mega Venusaur also is unable to do much to common Fire-, Steel-, and Dragon-types like Mega Charizard Y, Mega Metagross, and Dragonite, while also being weak to the plethora of Psychic-type Pokemon in the metagame like Tapu Lele, and Necrozma.