Per his request, I made my son's Perry the Platypus costume for Halloween. I couldn't have bought one if I wanted to, even online they were sparse and hideous. I'm all about sewing Halloween costumes, when hot glue guns, velcro, and unfinished edges are perfectly acceptable.
The head piece was made by using a baseball cap as a base, with foam used to shape the rest of the head and the beak. I could only find a black fedora, but, amazingly I bleached it and it turned out the perfect brown.
Quilted Platypus tail: