I would recommend Greninja if you're looking for a solid wallbreaker. Both Protean and Battle Bond are viable, but I would go with Battle Bond if what you're looking for is pure offensive potential. Base 132 speed allows it to outspeed almost the entirety of the metagame, bar scarf mons and a few megas, and base 153 special attack lets is hit like a truck.
Here's a common Ash-Gren set for you to start out with:
Greninja-Ash @ Choice Specs
Ability: Battle Bond
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Hydro Pump
- Dark Pulse
- Water Shuriken
- Ice Beam
Specs brings its destructive potential to near ungodly levels, meaning everything that doesn't resist this is getting blasted. Battle Bond makes it so that Water Shuriken becomes arguably the best priority move in the game, and Hydro Pump, Dark Pulse, and Ice Beam hit almost everything in the meta pretty darn hard. The only things you really need to be weary of is hyper defensive mons like Chansey, Toxapex, and Ferrothorn, so I would pair this with another offensive mon that can counter at least 2 of those.
Hope this helped!