Kabutops

Kabutops packs quite a punch (or... slash) with dual STAB on Water and Rock, a combination resisted by only a handful of Pokemon. With its STAB Aqua Tail, backed by Swords Dance, Life Orb, and rain, Kabutops can march through anything that does not resist Water, and it can deal with just about everything else with STAB Stone Edge. Kabutops is almost impossible to revenge kill as well--thanks to Swift Swim, Kabutops's Speed doubles in the rain, and it has STAB Aqua Jet to deter common priority users such as Blaziken, Hitmontop, and Absol. Kabutops can also function well outside of rain, as its base 80 Speed is relatively high even without a boost. If Kabutops gains a free turn, it is almost guaranteed at least one kill, especially under rain. One would do well not to underestimate it.