Kecleon @ Assault Vest
Ability: Protean  
EVs: 252 HP / 252 Atk / 4 SpD  
Adamant Nature  
- Knock Off / Power-up Punch / Fake Out
- Sucker Punch / Fire Punch 
- Shadow Sneak  
- Drain Punch

Role
Kecleon is your physical slow annoying Greninja copy. Special attackers will shiver when they see this behemoth on the field. It's fun to use, not gonna lie. 

Set
Its standard PU set with some additions. Knock off for the obvious reasons and power-up punch if you want to make its attack even stronger. Fake Out if you want to do some chip damage before going bonkers. Knock off even OHKOs marowak alola if it outspeeds it. 150 guarentees a OHKO and 120 attack gives it a 68% chance to OHKO (100% with rocks). Its priority allows it to change to types unaffected/resisted by the opponent's moves, for example shadow sneak makes kecleon unaffected by focus blasts etc. The combination of Dark and Ghost priority moves really opens up for some amazing mind games. Drain punch for recovery. No speed is needed because of the priority moves above. Fire Punch for Scizor if you dont have an answer for it (even though you probably run Ho-oh, Groudon or Arceus with Kecleon)

Calcs (offensive, inherited 150 attack from Groudon/Deoxys)
252+ Atk Protean Kecleon Knock Off (97.5 BP) vs. 248 HP / 0 Def Marowak-Alola: 356-422 (110.2 - 130.6%) -- guaranteed OHKO
252+ Atk Protean Kecleon Knock Off (97.5 BP) vs. 0 HP / 0 Def Tapu Lele: 246-289 (87.5 - 102.8%) -- guaranteed OHKO after Stealth Rock
252+ Atk Protean Kecleon Knock Off (97.5 BP) vs. 0 HP / 0 Def Nidoking: 240-283 (79.2 - 93.3%) -- guaranteed 2HKO (finish off with Sneak)
252+ Atk Protean Kecleon Drain Punch vs. 0 HP / 4 Def Swellow: 225-265 (86.2 - 101.5%) -- guaranteed OHKO after Stealth Rock
252+ Atk Protean Kecleon Sucker Punch vs. 0 HP / 40 Def Mewtwo-Mega-Y: 356-420 (100.8 - 118.9%) -- guaranteed OHKO
252+ Atk Protean Kecleon Sucker Punch vs. 0 HP / 4 Def Alakazam-Mega: 236-282 (94 - 112.3%) -- guaranteed OHKO after Stealth Rock (inherited 120 Def)
+1 252+ Atk Protean Kecleon Drain Punch vs. 252 HP / 24 Def Ferrothorn: 350-414 (69.4 - 82.1%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery (inherited 150 HP)

Calcs (defensive)
252 SpA Alakazam-Mega Focus Blast vs. 252 HP / 0 SpD Assault Vest Kecleon: 188-222 (58 - 68.5%) -- guaranteed 2HKO (or just sneak first hehe)
252 SpA Life Orb Tapu Koko Thunderbolt vs. 252 HP / 0 SpD Assault Vest Kecleon in Electric Terrain: 153-183 (47.2 - 56.4%) -- 84% chance to 2HKO (inherited 120 SpA)
252 SpA Choice Specs Swellow Boomburst vs. 252 HP / 0 SpD Assault Vest Kecleon: 222-262 (68.5 - 80.8%) -- guaranteed 2HKO (inherited 154 SpA)
252 Atk Choice Band Hoopa-Unbound Hyperspace Fury vs. 252 HP / 0 Def Kecleon: 191-225 (58.9 - 69.4%) -- guaranteed 2HKO (Kecleon as dark type after sucker punch)
252 SpA Life Orb Sheer Force Nidoking Sludge Wave vs. 252 HP / 0 SpD Assault Vest Kecleon: 172-203 (53 - 62.6%) -- guaranteed 2HKO (inherited 154 SpA)