One of my son's friends was having a birthday. According to my kiddo, his friend has apparently been pining for a Mario hat for years. A quick trip to the craft store and about 15 minutes, and his pining days are over! It was a big hit and "just what he wanted!"
I think if I did this again, I would cut out my own "M" to make it look a bit more authentic.
Using a cup or similar for your template, trace a circle on the scrap of white felt.
Center the embroidered "M" on the white circle.
(Optional - instead of an embroidered letter, cut your "M" out of red felt, then follow step three)
Slowly and carefully stitch around the "M."
*note* the "M" I used was an iron on, but I did NOT iron it - acrylic felt will melt and stick all over your iron ...ew!
Center the circle on the front of the hat, pinning carefully all the way around, turning out the inside facing if necessary.
Carefully stitch all the way around the circle. Mine was machine stitched, but you could hand stitch, too.