Ice King's crown

Ice King's Crown is the source of his Ice Powers. The crown is golden, topped with four points and adorned with three red gems. One of the gems within the crown protects Ice King from the evil brainwashing spells of The Lich.

In "Holly Jolly Secrets Part Two" it is revealed that long before the setting of the story, possibly before the Mushroom War, Ice King purchased the crown in Northern Scandinavia from "an old dockworker" when he was still a human named Simon Petrikov, as a part of his studies to be an antiquarian of ancient artifacts. He rushed home to his fiancée Betty and put it on to try and make her laugh. Upon wearing it, Simon experiences visions, which he frantically fought with and shouted at. He also underwent a personality change that he apparently couldn't remember afterward. He realised the crown was doing these things to him and took it off quickly, only to find his fiancée terrified and looking at him with "such contempt." She soon left him. After repeated exposure, the proto-Ice King developed his Wizard Eyes and his body underwent radical changes with subsequent use of the crown. His skin turned blue, his nose grew long and pointed, his body temperature dropped, his hair and beard grew long and white. After so much exposure to the crown he gained power of snow and ice, causing his home town to freeze solid around him unintentionally (which may have been how he created the Ice Kingdom). Simon realized that the crown's effects were becoming permanent, but knew he was "too far gone" to do anything. After the first time he put on the crown he started a series of videos chronicling what had become of him, in hopes that one day someone would help him to free himself from the things the crown was doing to his mind. The crown causes Ice King's emotional confusion and madness, as compared to Simon's calmness and intelligence. Simon's desire to make Betty (his "Princess") love him again surfaces in Ice King's desire to marry a princess.

In "What Have You Done?," Ice King mentions that he did not steal the crown, although he did make it with stolen magic. It is unknown whether this is true or not, considering Ice King's origin story revealed in the Christmas special. Adam Muto commented Ice King is an unreliable narrator and disassociated from the past of Simon Petrikov. So he may not remember where he got the crown and simply made up the fact that he made it himself.

Trivia

 * The gender-swapped version of the Ice King's Crown is a Tiara, as tiaras are worn by female Ooo royalty.
 * In the gender-flipped episode, Fionna smacks the Crown off of Cake's head saying "You'll catch her crazy!" Since Ice King wrote this fanfic, it is logical to assume that somewhere deep down in his psyche, the Ice King knows that the crown can drive someone mad.
 * In "What Have You Done?," the crown is shown to speak and feel regret in the scene where it cries on the shelf of penetence, on which its voice sound femine. Whether this proves the crown is sentient or is only the work of the shelf is unknown.
 * Jake has been seen wearing the Ice King's crown in the episode "Thank You," though it had no effect. This is because Jake is already magic according to Adam Muto. Since Cake was able to use the Ice Queen's Tiara, it is likely the Ice King is unaware of this fact or he made the fan fiction before "What Have You Done?."
 * Since Jake is shown to be immune to the effects of the crown it can be inferred that the crown can only affect those without magic, or it can only effect non-mutated humans, such as Finn.
 * In the episode Paper Pete,when Finn knocks all the books off the shelf one of the books pages has a picture of the Ice Kings crown.
 * In the short "Let's Work Together" Ice King's Crown has five points for a brief moment after he sacrifices himself to stop the Magic Freakin' Wand.