The Dragon Egg Merchant enables you to buy several essences for both your dragons as well as sell the Shadowmoon Dragon Egg, you pay him with Mark of the True Dragon.
Accessing the merchant[]
It can be accessed from the Dragon Isle; select the rightmost option (Merchant) from the icons at the bottom.
Your first dragon must reach at least level 50 to unlock Dragon Egg Merchant.
Items[]
Shadowmoon Egg (Price: 200 * Mark of the True Dragon)
Fiery Essence (Price 5 * Mark of the True Dragon)
Shadow Essence (Price: 10 * Mark of the True Dragon)
Black Bear Meat (Price: 5 * Mark of the True Dragon)
Horn of Awakening (Price: 5 * Mark of the True Dragon)