Sounds like you could put Defense of the Heart
to use. Maybe some Forbidden Orchard
s as well. The Orchard's will help you benefit from the Oath of Druids
while making sure you're opponents don't (as much), will help to activate Defense of the Heart
sooner (if people are holding back creatures), and can give you mana of any color to top it off.
Edit: Hydra Omnivore
is a great "bomb" for multiplayer as well. Should definitely consider fitting it in. Primeval Titan too. If you cheat it out, it helps you ramp up/mana fix for those hardcasts when someone removes the "stuff that sneaks things out of pockets".