To make Pikachu ears you'll need:
Yellow & black felt
2 Pipe cleaners or bendable wire
pen or pencil
Make a pattern out of paper & trace or print our pattern and trace.
Cut 2 of them out
With right sides together sew using a 1/2 inch seam allowance
Turn right side out
Fill with a little stuffing of any kind. Cotton balls or batting, etc
All done! Now just use a safety pin, or sew the base of the ears to the costume,
or glue to a headband.