At long last, we have created the Demon Core Ball & String from classic sci-fi novel Don't Create The Demon Core Ball & String

Core separate for easier printing.
Print face down, glue Core into Main Grip. Affix a string between Lid and Main Grip using a length and method of your choosing.

Keep away from children, animals, adults, or any other living beings.
(Seriously tho, the core might become a choking hazard if it comes loose.)