As far as I can tell, earth elemental is designed to rampage around destroying stuff like Godzilla. His mobility is terrible, which is why he needs the wizard to teleport him around. He costs 20 mana and requires a decent amount of support, so he's a huge investment early on and you're unlikely to have enough mana to summon more than one iron golem after that. Also, he's not psychic immune, so you need to be prepared to protect him from mind control and charm or to just summon an iron golem if you're fighting a forcemaster. (Iron golem is psychic immune)
To be honest, I'm not sure Earth Elemental even works that well in Standard Arena. Since he's meant to destroy enemy creatures and conjurations, you'd think he'd want to destroy the enemy mage's economy, (or at least their creatures and/or spawnpoints) before it can pay itself back. But that is very hard to do sometimes.
Now that I think of it, Earth Elemental might be better in Domination mode. Hmm.
