I would recommend Darksteel Ingot for mana generation too.
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I've been looking into creating an all green creature deck and Treefolk seems as likely a candidate as any. My concerns with this deck are that it looks a little slow. I was also wondering about taking out a land and the 4 x Worm's Tooth, adding a Reach of Branches and adding 2 x Cryptic Gateway to make playing creatures faster. Other treefolk that I wonder if they would be useful are: Woodfall Primus and Deadwood Treefolk.