Houndoom

Houndoom is the proud owner of the strongest Pursuit in the entire GSC metagame, with enough coverage and firepower to truly take advantage of Pursuit's utility. While other Pursuit users fail to do notable damage or even force out their targets for said Pursuit, Houndoom's strength forces Ghost- and Psychic-types to choose between getting 2HKOed by a STAB attack or potentially fainting to such a strong Pursuit. Combined with good neutral coverage in its STAB types, good Speed, and even better Special Attack, Houndoom is very difficult to switch into and out of overall. Houndoom's typing also makes it the best offensive check to Jynx and Exeggutor by resisting both of their STAB moves and having a pick of super effective STAB attacks to hit back. It can even run a Sunny Day set to become even stronger. However, Houndoom's low Defense stat means that even neutral hits can 2HKO the poor dog. Houndoom is also walled by very common Pokemon, most notably Snorlax and Tyranitar, and can struggle to achieve proper 2HKOs against some of its more valuable targets. Regardless, Houndoom's combination of utility and power makes it an addition worth considering.