I ran
Hydra Broodmaster for a while, and was really high on him in the beginning, because in a game where you're not too far behind and aren't in danger of dying, he can plop an impressive amount of power onto the board. However, he's lacklustre in most other scenarios; he has a huge 'echo' cost, takes a while before he can stabilize the board, doesn't block flyers, doesn't himself have evasion, and isn't Wrath-proof. There were a lot of games we played where its owner just didn't have time nor space to pay for monstrosity, and a vanilla 7/7 for six isn't the best rate in the world.
Having said all that, green is pretty thin on cubeable six-drops, so I would encourage you to try him out yourself if you're at all curious!