Having access to a cnc gives me inspiration to many things. When working on my Doll High Chair with wedged mortise joints I thought it'd be cool to give a 'client' a mallet with the chair to assemble it ... just like you get the hex key from IKEA every time you buy something. Thus the mallet should be as easy to build as possible.
My first attempt is very close to this goal. Cutting four parts from 10 mm material, glue them up and you are good to go. A little roundover with the hand router improves the handle significantly and does not take much time.
I made a second version to take care of the classic interpretation using different wood. A high quality wooden mallet should have a handle from ash-tree and a head out of white beech. Lacking those materials I choose oak for the handle and acacia tree for the head.
I have not tried to print the parts as I dont' have a fdm printer. Further I would be worried about the strength (and the weight) of a printed mallet.
Visit https://www.zenziwerken.de/en/ for more interesting designs.