Step 4: Finishing touches
Have your hat inside-out.
Grab the bottom inch-and-a-half or so of the hat and fold it up, around the "outside".
You're going to hem this thing, so make sure the raw edge is on the inside of the hat, once it all gets flipped right-side out.
Hem with a large zig-zag stitch all around. (This allows the cloth to retain some stretch without tearing the hem-thread.)
Flip your hat right-side out. You're almost done.
Do you need to add a muzzle, eyes, or other facial features to the hat?
Grab your felt. Cut it to shape. Sew it on to the outside of the hat.
Add eyes. A nose. Stuff.
Now trim all the extra thread and stuff, clean up your workspace:
You've got yourself a hat.
Here are some additional ideas:
Roman Centurion Helm
Greek Corinthian Helm