By survival means, the only way to obtain Jelly King's Crown is by defeating Jelly King. Once defeated the Jelly King, a chest containing it will spawn in the adjacent room to the boss room, the loot room. The Jelly King's Crow will come in a Marshmallow Chest along with other good and rare items such as enchanted Caramel Bows, Trampojelly Boots, Jelly King's Wand, and more!
Jelly King's Crown is used to show that the player that is wearing it had experienced the Jelly Dungeon and defeated the Jelly King.
Jelly King's Crown