The Ice Queen's Tiara is a golden tiara belonged to the Ice Queen and an object in a fanfic written by the Ice King in the animated series Adventure Time. The Ice Queen has a tiara, similar to the Ice King's Crown, only smaller. The most notable difference is that it has 5 points rather than only 4. Just like her male counterpart, her powers are contained in it. It could give anyone the power over the element of ice, as shown when Cake put it on and blasted the Ice Queen with a snow blast.
It may or may not cause insanity when worn, based on the Ice King's origin story, though Fionna told Cake not to wear it because she "might catch her crazy." This indicates that the Ice King knows that the tiara/his crown causes insanity.