Once upon a time, in the ancient Da Lonsan, a demon was banished out of a ruler's body and sealed into a magical gold box that was then cut into several pieces as to never free the demon ever again.

Solving the puzzle that forms the box, if all 16 pieces are available, is the attuning process and requires a DC 25 Investigation or Arcana Check (a natural 20 on this check automatically succeeds). The process takes at least one hour, as the pieces change their shapes through the means of illusion magic while it is in an unsolved state. This check can only be attempted if an attunement slot is available as the puzzle pieces repell eachother otherwise.

Upon completion, the box binds to the creature that solved the puzzle as a chain forms around the neck of the creature, forming a necklace. It cannot be unattuned or taken off by any means short of a remove curse or wish spell.

The box is a sentient magic item holding Xorrick, a chaotic evil demon with the simple goal of causing carnage and confusion as well as winning contests and games against anyone and anything. It has an intelligence of 18, wisdom of 22 and charisma of 16. Xorrick has a +12 on any game-related check, also serving as a modifier for deception, insight, and sleight of hand. They gain advantage on gaming set checks. Xorrick can communicate telepathically with the owner of the box as long as the owner speaks at least one language. Xorrick has blindsight up to 10ft as well as hearing from the box, however, while a creature is attuned to the box, Xorrick gains access to all of the creature's senses. It can understand and speak the following languages: Abyssal, Terran (Primordial) and Lonsanian. However, while not possessing a creature, Xorrick can only communicate telepathically with the creature currently attuned to the box. 

While attuned to the box, you are considered proficient with all gaming sets. You can use an ordinary deck of playing cards or set of dice to make a ranged weapon attack. This weapon counts as versatile, with a range of 30/60. The attack counts as magical for the sake of overcoming resistances. 

Possession. Xorrick is a demon trapped in a tiny box, they will use any chance to get out, even if it is only temporarily. As an Action, up to a maximum of five times a day, Xorrick can attempt to possess the current owner of the box, Xorrick makes a Charisma check of +5 opposed by a wisdom saving throw of the owner. On a success, Xorrick possesses you, until you repeat the save and make it, contested by Xorrick's Charisma check. This save is, in combat, repeatable once on each of Xorrick's turns, while out of combat, once every five minutes.

Possessed. While Xorrick possesses a creature, Xorrick can cast disguise self and will do so to make the hair of their possessee stand, as well as dye it blonde. Xorrick can use all features mentioned here, but none of your class features, while also being able to benefit from your senses, access your recent and surface-long-term memories (people you know but no details or secrets for example). Xorrick shares your initiative and physical stats during the possession. 

Master of Cards. Xorrick can magically conjure up a deck of illusions that can be dismissed from anywhere at will. There can only be one deck at any moment. It automatically regains all used up cards at dawn, and disappears back into its pocket dimension if it is more than 20ft from the box' current owner for a minute. You gain access to this ability if Xorrick allows you to, having to accept it every time you want to dismiss or conjure the deck of cards. Xorrick can dismiss or conjure the deck at the next free location close to you within 20ft or into the currently attuned creature's hand, at will, even while not in control of the creature's body.

Labyrinth And Eternal Prison. The box is a magical prison for Xorrick, design in a mazelike structure. While Xorrick possesses a creature, the creature's soul is trapped in this maze, while also being able to use their Action to see and hear through their real body's senses.