Print octopus costume pattern, enlarging to desired size. Trace and cut pieces from fabric as instructed in the pattern. Be sure to place the pattern for the back piece on folded fabric, lining up one edge with the fold, as indicated.
Place pupils in place on whites of eyes. Iron each eye onto the right sides of the outer hood (head) pieces.
Pin together two sides of the outer hood (head), right sides facing, and sew along outer edge with a 1/2-inch seam allowance. Clip into seam allowance with sharp scissors all around the curves, being careful not to cut into the seam. Turn outer hood right side out and press seam open.
Repeat Step 3 with the inner hood pieces. Pin raw edges of inner hood to raw edges of outer hood, right sides facing, and sew with a 1/4-inch seam allowance along hood edges, leaving the bottom (neckline) open. Turn right side out and press, then edge-stitch along seam with a decorative stitch.
The cape portion of the costume is made from three pieces sewn together along the shoulder seams. Unfold the back piece cut from the outer (teal) fabric. Pin the straight edge of each front piece to each straight edge on the back piece. Sew along these edges with a 1/4-inch seam allowance. Press seams. Repeat for the front and back pieces cut from the inner (polka-dot) fabric.
Place the sewn cape pieces on top of each other, right sides facing. Sew along edges and around tentacles with a 1/4-inch seam allowance, leaving neck open. Turn right side out and press.
Stuff the head and cape pieces with polyester stuffing, using chopsticks to push stuffing down into the tentacles.
Pin and baste raw edges of the hood neckline and body (cape) neckline together on what will be the inside of the costume. Center length of bias tape along neckline, fold open end of tape over raw edges, and baste in place. Beginning at one end of bias tape, machine-sew open end together along edge, continuing along neckline and through to other end of bias tape. Remove basting stitches.