I have to second complete legitimacy on Tangrowth: it's definitely among the most dominant Pokemon in RU, and likely the absolute most dominant. Both of its offensive stats are superb, while its physical bulk is through the roof. Thanks to Regenerator, it can easily switch in and out throughout the battle. It functions marvelously on offensive, balanced, and stall teams, giving it outstanding versatility. With Sleep Powder, it can even cripple a potential counter on the switch. Furthermore, its partner in crime, Slowking, can also succeed on offensive and defensive teams, allowing the duo to regenerate together effortlessly regardless of playstyle. Both of them even function well under Trick Room, which is a common condition in RU (Slowking can even set it up ^.^) If your team lacks an answer to TanKing, or even just Tangrowth itself, it'll be almost impossible to succeed on the ladder. It's a truly devastating Pokemon, and I would argue it's the most dominant force in the tier.