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Honestly, I've just been running a simple SubPunch set with good success
Adamant, 248 HP/252 Atk/8 Def
Focus Punch
Leech Life
Substitute
Bulk Up
Leftovers/Fightnium Z
Ideally, you try and switch into a physical attack he can easily tank, or pivot to him, I like to use Parting Shot A-Persian for this, as the debuff will often force switches. Depending on how you get in, you can either throw a sub up, bulk-up to take the incoming move, or throw a punch on the switch. Leftovers is the ideal option for survival, however, I've had good use from Fightnium-Z, as you can use it with Bulk Up for an immediate +2 Attack, or for All-out Pummeling if you want to nuke something.
However, I don't know if it's a glitch on showdown, or if this is how it works in-game, using All-out Pummeling with Focus Punch, for some reason, still makes you tighten your focus and become susceptible to flinching.