To make a shark costume, decorate a gray hooded sweatshirt with white fleece or felt, teeth and a fin. Pair the decorated shirt with matching gray sweatpants or slacks.
A shark costume can be made without having to do a lot of sewing.
Step 1: Make the fin
Put a ball point needle in the sewing machine. Cut a white triangle, about 1-foot tall. Sew around two sides. Stuff foam in the fin, making it about 1-inch thick. Stitch the open edges to the sweatshirt's back.
Step 2: Make shark teeth
Cut 3-inch strips of white, long enough to cover the front edge of the hood. Next, cut 1-inch zigzags on one edge of the strips. Overlap the flat edge of the strips with the inner edge of the hood, and stitch the teeth in place.