9/9 trample whenever you can actually cast it!

Even for cmc7 that seems slightly excessive. (Is this actually a common, or predating 'no rarity specified'?)

Hmm. I'm currently comparing this to Enormous Baloth in my mind, which could probably pose as a common right now. A 6/6 that becomes a 9/9 with Hellbent is probably fair. It's really only going to be used with new players and limited, and Hellbent might be tricky even after casting your giant 7-cost dude. Trample, however, is probably too much to ask for. A gigantic 9/9 trampler would be cool and fair at first... but I wouldn't want this to be the way that green wins every game in draft. It would get predictable. We all stall, then I get my giant wurm and the game is over in two swings. That's a one card strategy... which prefer not to see in a draft.

I think jmg's got a good point there. Green gets big creatures at common, and big creatures that trample, but not big creatures that trample at common.

The biggest common creature seems to be Ulamog's Crusher, and the biggest trample creature seems to be Yavimaya Wurm. I'm not sure 6/4 doesn't count as "big" at common, but I agree 9/9 is probably too much. (Even if it's not too strong, there's too much variance.) This would be a fine uncommon, or if it was a couple of mana cheaper and smaller in size, could be fine as a slightly-better-than-average-green-wurm.