Goblin Essence allows the player to change the race of their character to Goblin. Players using a Goblin may not be Scouts or Mages. However they may still use magic using prestige classes such as Pyromancer. The following mosnters drop Goblin Essence at these rates according to the Spy ability.
Goblin Stonecrusher drops it at 0.001%
Goblin Siren drops it at 0.001%
Goblin Shaman drops it at 0.001%
Goblin Ironclad drops it at 0.001%
Goblin Gladiator drops Goblin Essence 0.001%
Goblin Karegu drops Goblin Essence 9.09%
The Cogent drops Goblin Essence 5.5%