Some people might call me crazy for saying Skarrgan Skybreaker is worth looking at. It's very situational and very horrendously useless if you can't deal damage to your opponent before playing it.
I like this card a lot. Sure, it may be difficult to use and all, but you will surely be rewarded for your efforts. Laying a card like this down with Bloodthirst would probably wreck the game entirely.
As it is, it's pretty useless. 7 mana for a Fling-able creature that can only deal 3 damage if you can't somehow deal damage to your opponent by then. But if you can get the bloodthirst on, Skarrgan Skybreaker looks like a card deserving of rare. Fling-able. 6/6 body. Essentially unstoppable 6 eventual damage.
Chances are that if you are playing RG casual, you would have cards in your arsenal like Viashino Fangtail to assure you of your 1 damage to switch bloodthirst on. Lay this down nicely, and you get a 6/6 with Fling on it. Now, all you have to do is add more power to it. The most obvious way would have to be Loxodon Warhammer.
The Warhammer would immediately change things. Now, you would have a 9/6 trampler which you could Fling! If unchecked, you could gain 9 life while dealing 18 damage to your opponent, which would leave this opponent within Shock range (in most cases, he should be dead since you did have a Viashino Fangtail or Leyline of Lightning. ;) )
Skarrgan Skybreaker is a cool card. However, I'm talking about a very situational occurence. It can become a chump blocker; with its sac ability, it can probably deal with Jitte while still making sure your eight mana went somewhere.
Not to say that it can be considered for competitive play, but I would most certainly place it in my casual R/G to ensure I win. :D