I wanted to make 2-thumbed mittens for the various little-ones on my Christmas list this year. That way it wouldn’t matter what hand the mitten went on, and they would double as puppets if you used your pinky in the second thumb-hole.
I couldn’t find a pattern for such, so I took the pattern I found on ravelry from http://www.freevintageknitting.com/mittens/615-mittens-pattern.html and added the second thumb and edited to make the thumbs a bit more defined from the body, knitting in various 8ply yarns on 3.25mm double pointed needles. Then added the decor pieces (using various needles listed above) to make them look like characters from Yo Gabba Gabba! Muno and Brobee have been completed, Toodee is on the needles now!