Terastodon, Woodfall Primus, and Primeval Titan are probably the best cards for the "big green creature" role, but Simic Sky Swallower and Broodmate Dragon can serve the role as well, although they require greater deck manipulation to be able to hard cast should you draw either of them before finding your Natural Order
However, the reason Early Harvest doesnt see more play is because it only lets you untap basic lands
As far as strategy goes if you are using more than one Espeon in your deck or another Eevee-evolution in your deck it would only make sense to have Espeon in your deck so that that other Eevee evolution would have 20 more hp
Booster packs with the logo on the bottom of the pack are called Shadowless booster packs
Take proper care of your cards to maintain their value
To counteract this, it can be a good idea maindeck backrow removal cards such as Twin Twisters or Cosmic Cyclone