Tips for a unit no player in their right mind should be playing right now :P
Okay, so ele works but only sort of :P
I'll just direct you to this page for tips on mining with chomplers as there's little point in saying it again: http://forums.stickpage.com/showthread.php?75717-Miner-tips
One key difference is that Earths need to turn into Chomplers first, which gives you some room to use the health pools if you can before transforming or use of the transforming to remove effects.
1. Earths move faster than Chomplers so move them as close to gold mines as possible before making the unit transform when creating miners out of your base - you'll want to send the transform command earlier than that and give yourself some leway in laggy matches as losing potential mining time from lag is worse than gaining a tiny bit of movement efficiency.
2. Earths can stun chain a unit entirely with 3 and nearly perfectly with 2. You must adjust the timings of the Earths by moving single ones around to get the 'lock' on a unit, or if you can afford it you can use a water to pin units down to then keep pinned with Earths.
3. Earths have a very slow attack animation and the opponent will probably be able to run past them while your Earths are in small numbers. Placing Earths on both horizontal sides of a unit can help prevent it cheesing you.
4. Earths can be sent into combat in the early game to be used as a 1.5hp sheild then garrisoned and turned into miners as they return to your base to recycle them without waiting for them to heal up. When pulled off this gives you a lot of free hp to use in combat whilst also aiding your eco - at the cost of vulnurable chomplers and risk of throwing away your eco growth if your retreating Earths die too often.
This technique is most rewarding when you have fires or airs you need to shield for so they can get into attack range, and if the opponent has minimal ranged damage you can consistently pull off this technique. It gets very risky however once the opponent has a 3+ archers and the Earths cease to offer much protection before you need to retreat them.
Via this method you can constantly dive a castle archer extremely early in the game as long as your opponent cannot build up much army: www.stickempires.com/play?replay=replay6323031&version=2.08
When you have Airs/Cycloids and are tanking Castle archer hits you can let the Earths get extremely low and use the Air/Cycloid to take the retreating shots. Likewise you can shield archer shots with a Fire if you need to in order to keep a retreating Earth alive.
5. Transforming units cures poison and burn DoTs. This can be used on Earths by making Trees to prevent a poison DoT claiming a Water or Earth and also on Earths you have retreated out of combat but that will not last through the DoT to get back to your base - making them into Chomplers to keep them alive. Keep in mind that transforming Earths can still take damage from units. Admittedly the Chompler may take a long time to get back to your base and will probably still die if you are retreating (because Chomplers are slow), but unless you need the pop space you still gain from keeping a unit alive that would have died to a DoT.
6. In theory you should be able to command an Earth to transform to prevent the pull if you see it getting targeted by a Marrowkai reap but all this does is make the unit die while it is close to your units rather than further out, so both opportunity and gain are tiny. If you're still relying on Earths when the opponent has Marrokai you're also probably doing something wrong. - It might have a use in DM starts occasionally.
7. Stacking Earths in the build queue to make them all into miners is more efficient than Chaos or Order because the 4 seconds your Earth spends transforming also is used to buy the next Earth, meaning that you literally can spam miners faster than the other two empires if the game ever goes 'peaceful'.
