Slowbro (M) @ Leftovers
Trait: Regenerator
EVs: 252 HP / 252 Def / 4 SAtk
Bold Nature (+Def, -Atk)
- Scald
- Psychic
- Slack Off
- Thunder Wave
I'd hesitate to say that this is a fully fledged counter, because it cannot come into Blaziken's attacks, and expect to live the following turn. This is about as close as it gets, this checks Blaziken, assuming that you've just beaten Scizor, this can come in, use Psychic and finish off Blaziken. Shadow Claw is a solid 2HKO
That's a +2 LO Shadow Claw to Slowbro, not a OHKO, even after Rocks. Only other way is to revenge it with Excadrill or Aqua Jet from something like Azumarill. Other than that, nada, at least nothing I can think of, off the top of my head.678 Atk vs 350 Def & 394 HP (70 Base Power): 252 - 298 (63.96% - 75.63%)