Zargerth

I've been playing version 5, first at Reborn difficulty and then in Insane mode. Reborn difficulty has been useful for getting to know the leaders and their teams/strategies, and thus playing Insane mode hasn't been all that difficult now that I know what to do against them. I had to train some new Pokemon for some of the gyms, luckily it doesn't take that long. I would've had much easier time with the Water type leader if I had bred my Lombre, but I caught a male...also, Narcissa was already on Reborn difficulty the bane of my existence, I beat the Water type leader before her. Other than that, I've beaten the gym leaders in Insane mode on my first try or so.

Shade's Gengar knows Shadow Claw, so yes it knows physical attacks. If you're willing to use your Focus Sash, you could just lead with Shuppet (let it hold the Sash) and use Destiny Bond on the Garchomp. Unless you already have replaced it, Shuppet should know DB without any need for Heart Scales / level ups. You might be able to use Charge Beam and take the advantage of the field effect in play.