FISHIOUS REND MEGA SHARPEDO
Availability: Early, before the third gym at Route 4.
Stats: Scraggy has solid Attack and defenses, the latter of which can be further boosted by Eviolite. Upon evolution, its defenses overtake its Attack, meaning it remains bulky before and after evolution. It is fairly slow though, meaning it often has to take hits (which it does well) before it can attack.
Typing: Dark + Fighting make a great combo, as only Heracross and Toxicroak resist them, both of which are only seen like once. The typing also grants it only 2 weaknesses in exchange for very relevant resistances to Ghost and Dark as well as a Psychic immunity.
Movepool: Scraggy starts off with Faint Attack and Headbutt, then promptly gets Brick Break at level 20. It's pretty smooth sailing from there as Scraggy can single-handedly take on almost any opponent. It gets Payback, Hi Jump Kick, and finally Crunch right before evolution. Scraggy's movepool consists of high power moves and is incredibly self-sufficient, meaning it doesn't really need TMs or tutored moves (though Drain Punch is an incredible move for Scraggy/Scrafty to learn), but you can teach it some temporarily useful moves like Rock Smash before getting Brick Break, Dig, Rock Tomb and even Ice Punch.
Major Battles: With access to Dig and Rock Tomb, Scraggy can take on Elesa easily. Its Fighting attacks do well against Clay's Krokorok and Excadrill. Crunch can take out Skyla's Swoobat but otherwise try to steer clear of Flying-type moves. With its bulk and strong attacks, Scraggy can go head-to-head to Drayden, only fearing Druddigon's Revenge. Scraggy manhandles Marlon's Jellicent and stomps both Zinzolin and Colress, while taking on any of Ghetsis's team bar Toxicroak. Scraggy has a positive matchup against 3/4 of the Elite Four and take on most of Iris's team.
Additional Comments: Scraggy may be able to tank well, but its low speed means it can't exactly do this forever, but it is still one of the best in one-on-one fights. As for abilities, either Shed Skin or Moxie can work on Scraggy: the former wards off status conditions (most commonly seen by Colress), while the latter is generally better as it allows Scraggy to truck through trainers with large parties, which are the more important fights.