Details: One of the thirteen Special Trainers you will encounter at The Battle Tree after completing certain streaks with the multiple of ten in single player modes or team up with in multi-Battle mode is Grimsley, the man who showed you how to ride on Sharpedo on Ula'ula that just so happens to be one of the Elite Four of the Unova Region. His possible Pokemon resemble that of his team from the Unova Region, specializing in Dark Type Pokemon.
Possible Pokemon:
Houndoom (Air Ballon): Flamethrower, Shadow Ball, Sludge Bomb, Will-o-wisp
Houndoom (Houndoominite): Fire Blast, Dark Pulse, Solar Beam, Sunny Day
Tyranitar (Chople Berry): Rock Slide, Crunch, Earthquake, Dragon Dance
Tyranitar (Tyranitarite): Stone Edge, Earthquake, Ice Fang, Payback
Sharpedo (Sharpedonite): Crunch, Ice Fang, Aqua Jet, Poison Jab
Sharpedo (Focus Sash): Ice Beam, Hydro Pump, Dark Pulse, Protect
Absol (Focus Sash): Night Slash, Zen Headbutt, Sucker Punch, Play Rough
Absol (Absolite): Sucker Punch, Megahorn, Play Rough, Stone Edge
Honchkrow (Darkinium Z): Psychic, Dark Pulse, Swagger, Shadow Ball
Drapion (Scope Lens): Cross Poison, Night Slash, Fire Fang, Earthquake
Drapion (Razor Claw): Cross Poison, Night Slash, Earthquake, Swords Dance
Liepard (Red Card): Foul Play, Sucker Punch, Sand Attack, Thunder Wave
Liepard (Focus Sash): Dark Pulse, Shadow Ball, Grass Knot, Nasty Plot
Scrafty (Fightinium Z): Substitute, Payback, High Jump Kick, Focus Punch
Scrafty (Leftovers): Bulk Up, Payback, Protect, Drain Punch
Bisharp (Chople Berry): Iron Head, Night Slash, Low Sweep, Sucker Punch
Bisharp (Focus Sash): Taunt, Sucker Punch, Metal Burst, Iron Head