King Yolkar

 is an NPC found in the Goblin Holdout in the Crystal Hollows. When talking to him and giving him, he will give the player the Potion Effect for 20 minutes, allowing the player to sneak past the Goblin Queen's guards into the Goblin Queen's Den to obtain the Amber Crystal.

Trivia

 * His name may be based off of the word yolk, the inner part of an egg, which may explain his constant hunger for Goblin Eggs.
 * The effect can be toggled on and off using Booster Cookie.