The Earth Dragon only spawn in The Cavern Of Coal. A massive room this biome has a crater in the middle of it when you are within 10 blocks range of the crater. The Earth Dragon will fly out you can ride the Earth Dragon with the Reinforced Dragon Saddle.
This creates a dirt wall (3 long, one high). After a while, you will be forced to divert your attention to the walls, as they will become a major hazard.
Several stones are hurled from it's maw, and if one hits you, it does 30-90 damage, and knocks you back six spaces.
If you get to close, you get hit back sixteen spaces, and take 10-25 damage.
The Roar does no damage, but knocks you back twenty spaces.
You kill it, and it drops the Earth Egg, and a full-health diamond edge.
You must feed it with two Stone per in-game day. Otherwise, it will become feral and hostile. As it is Purebred, you get an egg back. There is an exeption for this in Multiplayer; see Feeding Dragons.
When riding the Earth Dragon click F to use your primary attack "Stone Breath" and click G to use your secondary attack "Wall"