Amoonguss

For a long time, Amoonguss was not a very useful Pokemon on the competitive scene. It was cursed with mediocre stats in all areas bar HP, and its typing is not exactly ideal offensively or defensively. Amoonguss's movepool isn't anything to write home about either outside of Spore, which meant it had little to work with. It was also as a result almost entirely outclassed by numerous Grass-types such as Roserade and Shaymin. All of these bad points led to Amoonguss never seeing any real use.

However, with the transition to BW2, Amoonguss has gained an ability that gives it a new lease on life: Regenerator. Thanks to this wonderful ability, Amoonguss can constantly recover itself upon switching out, while its access to the rare Spore, surprising bulk, and resistances to Water, Electric, and Fighting make it a legitimate threat in UU. Amoonguss's bulk and typing allow it to take on numerous threats in the tier such as Kingdra, Shaymin, and Mienshao. Its movepool, albeit small, has just enough tools for Amoonguss to work with, such as Spore, Clear Smog, and Stun Spore. Despite its middling offensive stats, weaknesses to Fire, Ice, and Flying, and competition from other Grass-types, Amoonguss is still a solid Pokemon for use in UU.