Source: Xanathar's Guide to Everything

Wondrous item, common (requires attunement by a wizard)

This antiquated, cone-shaped hat is adorned with gold crescent moons and stars. While you are wearing it, you gain the following benefits:

  • You can use the hat as a spellcasting focus for your wizard spells.
  • You can try to cast a cantrip that you don't know. The cantrip must be on the Wizard spell list, and you must make a DC 10 Intelligence (Arcana) check. If the check succeeds, you cast the spell. If the check fails, so does the spell, and the action used to cast the spell is wasted. In either case, you can't use this property again until you finish a long rest.