I used Hungering Claw, Sanctum Cub, Manafiend (any should work)
Shadow Shock (x2), Doom, Shadow Shock (Claw dies) Leap, Black Claw (swap Cub for Manafiend) Surge of Power (Manafiend will die forcing Cub back out) Leap IF Ruinhoof does not die to Surge/Doom exposions
I have a feeling most hard-hitting pets will fare well in the first spot of this strategy. I did it with Brightpaw (Prowl > Pounce for a big hit, taking Ruinhoof to half health, at which point the Broom & Eye could finish it off), but pets like Legs and Lesser Voidcaller might also be able to do the job.
I found Jade Owl (2,1,1) to be helpful here because you can use Adrenaline Rush on the first round of Chew which increases your speed so you can use Lift-Off on the second round of Chew and miss both hits. Plus, you get the additional hit from Thrash for attacking first.
Start with Legs
-Pump, first use
-Pump, second use
-Surge of Power, Legs will die, Bring in Manafiend
-Surge of Power, Manafiend will die, Bring in Arcane Eye
-Mana Surge, Ruinhoof died here