I started playing Face Shaman at rank 2->rank 1 because it's the last day and I wanted to get legend, but then I dropped back to rank 2 so I reverted back to my Astral Communion deck.
Anyway.
Rank 16-Legend in basically no time playing 99% strictly Astral Communion.
Grommash was used as a finisher for most warrior decks, 10 damage/10 mana charge/2 cards (unless you had Death's Bite ready to go).
Malkorok would be an 8 damage charger with 2 cards, but would also give you a weapon. If they have a small taunt up, the weapon could handle that, whilst Malkorok goes face.
In the same way as Grommash, Malkorok can also use Ysera's nightmare too.
I mean, I can't really see him being useful at all. Really weak stats for a 7 drop. That is basically the only scenario I could ever see him having a use in constructed.