My thoughts:
Coiling Oracle needs blue so that's out. Sedge Scorpion is bad. Hornet Queen, while expensive, isn't a good finisher. Biorythm isn't that great for 8 mana. It's a big effect of course, but it won't win you the game and something that costs 8 mana should win you the game.
With all of the mana that the deck produces you should put in a few more higher-cost things:
- Terra Stomper
- Overrun
- Terastodon
- Gaea's Revenge
- Kamahl, Fist of Krosa
Edit - Biomantic Mastery
Harmonize would also be good as a 4-of in this deck as Mono Green really lacks card draw.
The deck also absolutely needs some form of protection.
- Wrap in Vigor