Step 1: What You'll Need
Sewing Pattern "for a shark body" (we used an old out-of-print patter McCall's 4529. I recommend Simplicity 2068, 2070 or 2788, or McCall's 6812)
1/2 inch thick Foam
Brown Fabric (for lining shark body)
Red Fabric (for lining shark head)
Sewing Machine (or needle and thread)
Paper or Newspaper to Make Head/Tail Pattern
Hot Glue Gun and Hot Glue Sticks
Big Black Pom-Poms
Step 2: Make the Body and Arms
For the arms, you can follow the sleeve directions for the sewing pattern, or you can sew long rectangles of fabric and use Velcro to attach them to the body (the rectangles will run along the top of the arms). We did this method (again, for toddler-dressing-convenience/dismantle) and cut and sewed the edges of the 'sleeve' bottoms to be pointed like a shark fin. A tube of elastic was sewn to the ends for my niece to stick her hands into, to keep her 'fins' in place.
Step 3: Make the Tail
I drew out a shark-tail shape, then two right-angled triangles, on newspaper for a rough pattern. One of these was fairly short - it would join the sides of the tail at the top, at the front. The other triangle was longer than the length of the main part of the tail, and would join the sides from the front to the fins. I sewed the top triangle to the tail sides first, stitched the tail-fin parts together, then sewed the bottom triangle piece to the bottom of the tail sides. I stuffed the tail with fiber fill, then stitched the two triangle ends together.
Velcro was later sewn to the bottom triangle and to the back of the body (again, for easy removal and so the body part of the costume could be used again as just, say, a jaguar).
Step 4: Construct the Foam Head
Step 5: Add Fabric/Teeth to Head
Step 6: Bribe Toddler to Get Them to Wear Costume
Originally the idea was to have her all in brown, but during the whole costume creation, she was pretty fussy and uncooperative. To get her to test-try on pieces, candy was involved. So when Halloween actually rolled around we were ready with bribery treats, but she got ready all on her own and was pretty ecstatic...so we decided not to test our luck and just let her stay in her current clothes with her costume over-top.
Teach toddler shark (dinosaur?) noises and let her loose (following her close behind).
Step 7: *Bonus* Accompanying Team Zissou costume
For the Team Zissou outfit, you need a light-blue/blue-teal collared shirt (my husband found one at a thrift shop) and matching pants (which likely are going to be scrubs. We also found ours at the thrift shop). I sewed blue strips down the sides of my husband's pants and shirt and along the shoulders. I added blue epaulettes and a pocket that I had previously stitched a Zissou patch to.
The patch was found online, as was the hat (it's pretty orange, I dyed it red) and the shoes ("custom"-made).
My husband and I made a simple gun holster out of stiff black fabric (which consisted off a large pocket and one horizontal and one vertical running band, all held together with Velcro) and the glock was just a toy gun we picked up at the dollar store.
Make sure to practice your exercises.