Essence

Essences are items that are used in the Trade Market. Currently, they can be obtained in two ways: through Monsters, for Attack and Damage essences, and through Quests, for Defense and Health essences. When traded at the Trade Market, they will upgrade your personal Runes in order to get bonuses to your stats for Guild battles and normal gameplay.

Essence Drops

At the moment, it appears that Essences will drop from monsters that have at least 300 million health. Additionally, monsters summoned through the normal Summon page will drop essences, while Festival monsters from either Tower of Transcendence will not drop essences. Monsters summoned in Guild Conquest do drop essences, though this functionality was not working properly at first.
For each monster that does drop essences, either Attack or Damage essences will be dropped (depending on the monster), and only one quantity will be dropped. It appears to drop after a fairly consistent amount of damage or stamina, so using smaller amounts of stamina will not increase your chances of getting more drops per stamina.
The above statement about stamina use is wrong.  Further research needs to be done to determine percentages of drop rate.
It seems that the game awards a quantity of essences after using 100 stamina on a monster. For example, one could do 2 50x power attacks and get 1 quantity of essence. This does, in fact, work with Generals that increase stamina usage.


Damage Essence can you get from

• Azriel
• Aurelius
• Jahanna
• Aurora
• Ambrosia
•  Azeron
• Fenix and many more 

   Attack Essence can you get from

• Alpha Mephistopheles
• Corvintheus
• Malekus
• Baal
• Alpha Bahamut
• Gehenna
• Glacius
• Typhonus
• Vermilion
• Kessaran        

Excavation Quests 

There are 4 new Excavation Quests available right now that will help you receive Defense and Health essences. They can be found in one of 4 quest areas: Land of Mist, Land of Water, Underworld, Mist II.
Energy used per level

• Level 1 Excavation: 300 Energy
• Level 2 Excavation: 400 Energy
• Level 3 Excavation: 500 Energy
• Level 4 Excavation: 600 Energy

Total needed for completion is 1800 Energy.

Land of Mist

• Level 1: Defense Essences x200
• Level 2: Defense Essences x500
• Level 3: Defense Essences x900
• Level 4: Defense Essence x1400

Land of Water

• Level 1: Health Essences x200
• Level 2: Health Essences x500
• Level 3: Health Essences x900
• Level 4: Health Essences x1400

Underworld

• Level 1: Defense Essence x205
• Level 2: Defense Essence x515
• Level 3: Defense Essence x930
• Level 4: Defense Essence x1450

Mist II

• Level 1: Health Essence x205
• Level 2: Health Essence x515
• Level 3: Health Essence x930
• Level 4: Health Essence x1450

 

 source :http://castleage.wikia.com/wiki/Essence