Tangrowth

Tangrowth proves to be a stellar, albeit uncommon, pivot in OU, thanks to an amazing ability in Regenerator that gives it passive recovery upon switching out, admirable mixed bulk when equipped with an Assault Vest, and solid resistances to common attacking types, most notably Water, Ground, and Grass, that let Tangrowth check many common threats, like Azumarill and Landorus-T. Tangrowth further separates itself from other defensive Grass-types, specifically Amoonguss and Mega Venusaur, thanks to its resistance to Ground, which makes it a far more effective check to common Ground-type attackers like Landorus-T, Excadrill, and Garchomp. Furthermore, Tangrowth makes up for its lack of offensive presence with its immense longevity and ability to whittle the foe down with moves such as Knock Off and Giga Drain, meaning that it will often outlast the foe if used effectively. However, Tangrowth is ultimately held back by its weakness to common attacking types such as Fire, Flying, and Ice, making it vulnerable to common attackers such as Talonflame, Tornadus-T, and Kyurem-B. Tangrowth also faces immense competition from its fellow bulky Grass-types, Amoonguss and Mega Venusaur, which boast useful resistances to Fighting and Fairy, alongside Spore and Thick Fat, respectively. On top of all this, Tangrowth is a relatively passive Pokemon, as its moves either have low Base Power, in the case of Hidden Power Ice or Hidden Power Fire, or come with unwanted side effects, in the case of Leaf Storm.