I made mine out of concrete pouring tubing (12" diameter) cut down to a 19" length and a shower curtain rod for the handle.
The handle, I covered with ducktape. The mallet itself is spray painted black and the ends are painted canvas and hot glued on.
Hi! If you can't tell from my username, I like Wonder Woman.
I'm currently in the middle of a costume build for her using wonderflex. I also drive a Wonder Woman themed car.