DIY Bowser Shell, Koopa Shell, or Turtle Shell Costume with FREE pattern

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When my toddler requested a Bowser costume for Halloween, I told her to pick something easier. We went with Luigi (CLICK HERE to see how I made her Luigi costume). When it was time to make our Christmas wish lists, she still really wanted a Bowser costume and I decided I would make time to create it. Bowser’s shell was the bane of my holiday sewing and this is not a beginner’s project. I am not really a pattern creator, but I had to make my own with this project. I was so glad when my DIY Bowser Shell was finally complete, but I was also sooo happy with the outcome. If you want to attempt one to make your little one happy with a turtle shell, I have included directions and my pattern pieces to get you started on this DIY Bowser Shell. CLICK HERE to see how I made the full Bowser Costume with all of the accessories.

Overview of the DIY Bowser Shell

Please read through the directions before starting. Once you see the process, you can print and assemble your pattern and gather your sewing supplies.

Supplies needed for this DIY Bowser Shell

In addition to general sewing supplies such as thread and a machine, you will need:

  • green fleece for the outer and inner shell
  • scrap of cotton lycra or old t-shirt for outer shell lining
  • white fleece for the shell border
  • white fleece for the spikes (spikes are optional)
  • tan fleece to go around the spikes
  • yellow fleece for the straps

I also used a zipper on my inner shell to turn the shell into a backpack. You will also need stuffing/fiberfill if not turning the shell into a backpack.

DIY Bowser Shell Pattern

In my search for how to make Bowser’s shell, I came across some directions on this blog post. Although I did not follow the exact methods in the linked post to create my shell pattern, the process was similar and it gave me a starting point. The FREE pattern linked below is for a shell in a size 4T-5T, but also fits my one year old and my 7 year old. Feel free to enlarge or reduce as desired.

This shell pattern is for personal use only. Please download for your own creations and please direct anyone who wants a copy back to this page to download their own copy.

The linked shell patterns are 1/4 of the shell front and back. The front is the one with a dart drawn on the pattern. Print out 4 and tape together to get a full pattern piece.

Outer Shell Cutting and Assembly

Outer shell piece and outer shell lining

Cut an outer shell in green fleece and cut a lining piece in stretch fabric. I used some scrap cotton lycra as my lining. You could also use an old t-shirt or anything else with a little stretch.

Trace the dart onto your outer shell pieces and sew on the lines to form the darts.






Put your two outer shell pieces wrong sides together and pin in place.

Draw 10 hexagonal shapes on the outside of your outer shell piece. There should be 4 down the middle and three on each side. Sew on your lines, securing the outer shell to the lining piece.  Ignore the single spike for now. I forgot to take a photo before I sewed that one on.






If you are making a regular Koopa shell or turtle shell, your outer piece is now complete. If you are making a Bowser shell, keep reading to see how to sew the spikes.

Spike Assembly

Trace 10 spike pieces onto your white or cream fleece. The pattern piece does not include seam allowances, so you will add that to the straight edges. I added 1/4 inch on mine when I cut them out. See image below.







Next take your tan fleece and cut a 1.5″ strip of fabric. I cut mine across the entire piece. You want your stretch to go along the length of the strip so it stretches easily.

Fold your tan strip in half. With right sides together, sew the tan strip to the curved edge of each of the 12 spikes using 1/4″ seam allowance. I just serged mine.








Cut the tan strip between the spikes to separate. Then fold the spike in half with the seam pressed up. Sew along your drawn stitching line and continue down the tan strip to the end. 







Flip the spike right side out and lightly stuff with fiberfill.








Attach Spikes to Outer Shell

This part was a little tedious, but it was much faster to machine sew them on. Center the spike in a hexagon on the outer shell and pin in place. When you pin it on, make sure the seam of the spike is facing down on the finished shell.

Carefully sew in the ditch on the seam joining spike and tan strip. As you sew, the tan strip will curl up around the spike.







To hide the seam on the tan strip, sew it down to the shell using a straight stitch.

One you sew on all 12 spikes, your outer shell is complete!

Inner Shell Cutting and Assembly

Cut your inner shell piece out of fleece. If you want to add a zipper to make the shell a backpack, also cut a lining piece out. If you are planning on just stuffing the shell, you do not need a lining piece for the inner shell.

Rather than give detailed directions on how to add a zipper, ikatbag has a tutorial here.

Attach Front and Back Shell

Serge or baste your inner and outer shell together, right sides out. If you did not include a zipper, leave an opening to stuff your shell. Then stuff your shell and sew the opening closed.

Cutting and Assembling the Straps

For the straps, I cut 4 strips of yellow fleece 3 inches wide. I cut my straps extra long, but for the included size, yours will need to be around 18″ long. Put 2 pieces right sides together and sew them on each side with a 1/2 inch seam allowance.

Next, flip your strap right side out and top stitch along the length of each side.

Attach the Straps

Baste the straps at the top of the shell. I forgot to get photos of this step, so the included images show the outer white edge of the shell already attached. Attach the straps before attaching the outer binding.

Next, use safety pins to attach the bottom of the straps to the shell around the angles around 4 o’clock and around 8 o’clock. Try this on your model and adjust until the fit seems perfect. My final straps measured 15 inches from the top to the bottom at the stitching lines where they were attached.

*Side note* I originally tried attaching the bottom straps at the bottom of the shell, but quickly realized this would not work. If you attach the bottom of the straps too low on the shell, they pull the bottom of the shell up when someone is wearing it.

Daily practice titles from Evan-Moor, trusted by teachers and ideal for students

Cut and Attach the Binding on the DIY Bowser Shell


This part was pretty tedious and I wish there were an easier way to attach the binding. Basically, I cut a strip of white fleece and attached it like bias tape, but then stuffed it while I was attaching the second edge. I did not get photos of attaching the binding, but VisibleBlue has some in her Bowser shell assembly directions here.


  1. Cut a strip of white fleece 4 1/2 inches wide. The stretch should be along the length, like bias tape.
  2. With the right side of the fleece on the backside of the shell, sew one edge of the white strip around the turtle shell. Leave room at each end to sew the strip together and cut off excess.
  3. Next, fold over a section of the edge (about 1/2″ wide) and pin down to the front side of the shell. Make sure your section is short enough for you to reach in and stuff. Sew this down to form the binding.
  4. Then stuff the section you just sewed.
  5. Repeat steps 3 and 4 until the binding is completely sewn and stuffed all of the way around.

Completed DIY Bowser Shell!








Your DIY Bowser Shell is now complete. If you are like me, you may hope to never sew one again. But, I will have to say this shell is well loved and played with on a regular basis, even months after Christmas.

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