The Earth deck is my favorite!

In the Gold League you need Lyanna in lvl 6, and it would also be very useful a Selenya (+1 arrows) that combines well with Earth, she is expensive but needs only 5 cards for level 3 which is the needed for gold league.

Earth cards that are important in my opinion:

• Flesh Golem / Stone Golem
• Earth Elemental
• Swamp Thing
• Wood Nymph -
• Javelin Thrower
• Mushroom Seer
• Brownie
• Goblin Sorcerer
• Magi of the Forest
• Spirit of the Forest - expensive one, but the most important card from Earth splinter.

Spirit of the forest is even good at level 1, because it is very fast and has a lot of HP (compared to other cards), but at level 2 she gains Tank Heal wchich is very useful.

And the spirit must be accompanied by a good centaur, because if Spirit without Centaur (or dwarven wizard) attacks Tree or Water elemental, this is just a wasted attack.

In the gold league if you can use it in lvl 3 then everything becomes even better as it gains the ability protect + 2 armor which helps a lot your cards against earthquakes and against arrows.

I hope this helps, good luck !