Houndour

Houndour has one purpose—to trap and eliminate Xatu with Pursuit. Since it is immune to Xatu's nearly unresisted STAB Psychic, takes little from Hidden Power Ice or Electric, and has a solid Special Attack, Houndour can consistently clear the way for teammates that are otherwise walled or annoyed by Xatu's presence, such as Primeape, Hitmonlee, Kingler, Gloom, and Weezing. Houndour's Fire Blast is also quite strong, being as strong as Rapidash, and it's faster than Pokemon like Weezing and Gloom, so even after it removes Xatu, it might still be able to force damage on the opponent's valuable defensive pieces. However, after removing Xatu, Houndour often does little else and is usually sacrificed for a free switch, as it is extremely frail, is relatively slow, is walled by other Fire-types, and takes heavy damage from Water-type moves, with Octillery even OHKOing it with Surf. Houndour often makes for defensively flawed teams, since it so often does very little compared to an otherwise better Pokemon once it is done trapping Xatu. This is not even to mention that some teams do not even use Xatu, in which case it can feel like playing a five versus six matchup. Houndour also struggles heavily against Pokemon like Dewgong and Stantler, further limiting what it can do beyond trapping Xatu.