Hello and welcome to my first instructable! I've made Harley Quinn's giant mallet for my daughter's Halloween costume. I've basically combined all the strategies I found online, with a few tweaks of my own. The total cost was about $80.

Step 1: Materials

I used a 3' long (7/8" thick) wooden rod for the handle. I found some roundish finneals to fit on the ends, to ensure the head would stay firmly attached. Any shape will do, as long as it gets wider in the middle.

I used 2" thick roll foam for most of the hammer head. I also used an 8 7/8" foam florists wreath on both ends, to achieve the comic curvature.

For the center of the head (which will provide all the stability) I used two 8" diameter (1" thick) hard foam circles.

This is going to require A LOT of duct tape. I used one and a half rolls of industrial sized silver duct tape. I had intended on using brown tape to decorate it, but decided later to go with spray paint, which was definitely a better choice.

A hot glue gun was my weapon of choice on this one, although wood glue or rubber cement might prove reasonable alternatives. I used about 20 or 30 hot glue sticks.

I used an Xacto knife to carve the harder foam, and an electric carving knife to cut the roll foam. Later, I used the largest pair of scissors I could find for some finer details.

Always have your trusty permanent marker with you at all times.

Step 2: Carving the Mallet's Center

Hot glue your finial onto one end of your rod. Don't skimp on the glue, this bond will be vital in the end.

Lay your 8" round on a flat surface and place the finial end in the middle. Trace with your marker around the edge of the finial and rod.

Carve a 1/2" deep area in the traced area. It's very important that both your foam rounds line up, so lay the uncarved one on top of the other, and mark the edges where the rod will sit. Trace and carve the other foam round, making sure that both rounds hit exactly the same height and angle.

Hot glue the rod into place in one of the carved rounds, allow it to set, then cover the entire carved area on the second round with glue. Quickly press the two rounds together, with the finial and rod inside. If there is any gap between the rod and the base of the round, fill it with glue.

Now we're going to duct tape this entire lollipop monstrosity. Wrap long strips around both halves, so the end result isn't going anywhere. Ever. Leave room around the base of the rod, to avoid creating folds near the handle.

Step 3: Creating the Mallet's Main Body

My roll foam was 27" wide, which gave me plenty of room to trace three 8" circles with a permanent marker. I used my duct tape lollipop as a template, then cut out six circles with an electric carving knife. Your circles are not going to look perfect, but it's not going to matter once we wrap everything in tape. I will admit, this is when I decided to aim for the cartoony curved look, as some of my circles were smaller around than others.

Line your circles up in two piles of three, and decided what shape looks best. Again, it's not going to be perfect, but it won't matter in the end. Apply plenty of glue to the entire area of one side of your lollipop, and carefully place your first foam circle. Repeat this process on the other side, alternating sides each time. This help keep your mallet balanced.

When you're done, you should have something similar to the bottom photo. Use scissors or a knife (electric or otherwise) to give your mallet its rough shape.

Step 4: Creating the Mallet's Ends

I added a slightly larger foam wreath to each end in order to create the cartoony curve. Before I attached them, I traced the inner ring onto my roll foam and cut out a circle to fill the center gap. I had to cut the circle in half width wise, since my foam was 2" thick and my wreath was 1" thick. I did this with a serrated kitchen knife.

Add glue to the entire outer edge of your roll foam circle, and firmly place the wreath in the center. Then glue the foam filler into the center of the wreath.

Step 5: Using More Duct Tape Than You Thought Possible

It's time to wrap this baby up. Start with your ends. Using 6 - 8" strips, place one end in the center of your foam filler circle and wrap around the edge, onto the main body. If you pull firmly, this will begin to create the curve on the ends.

Once both ends are covered, move on to the body. Take 12" - 16" strips, and wrap tightly around the circumference of your mallet head. Take your time and avoid wrinkles when you can, but don't obsess over it. You've got more to worry about.

Step 6: Decoration

I used textured outdoor spray paint, and applied it to the entire thing, pole and all.

I used red duct tape, split into 1" thin strips, to create the pattern on my mallet. Placed about 4" apart, and at the proper angle, they make perfect diamonds. Mine didn't turn out perfectly, but there's always next year.