I recommend you ditch Child of Gaea (I would avoid any card with an upkeep anyways) and put in a Civic Wayfinder. Also, swap out a couple of your {3} cost cards for a {1} or {2} cost, so you don't run the risk of getting mana-starved. You can never go wrong with Joiner Adepts, Quirion Elves, Wirewood Elves, and Leaf Gilders. And for a creature-heavy deck like this, Gaea's Herald is a good choice, too.
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I recommend replacing your Overgrowths with a few {0} casting-cost non-creature artifacts to make the most use out of Terastodon.