My kids love Adventure Time. They decided they wanted to be Finn and Jake for Halloween. The cartoon is pretty new and you can't find any Adventure Time stuff in stores so I had to make their costumes from scratch. Here's what I came up with for my daughter's Jake costume.
Step 1: How to Make Jake's Body
First, measure the wearer's shoulder width plus the length from the top of their head to mid-thigh, then cut 2 pieces of yellow fleece in those dimensions, rounding at the top.
Next, cut a long strip of fleece for the outside edge of the costume and reinforce it with 2 pieces of thick fusible web in the middle. You could also use cardboard. You'll need something sturdy to shape it in a dome above the head instead of letting it drape limply.
Starting at the midpoint of the long fleece piece and the top of one of the body pieces, sew 3/8 inch along the edge. Next, go back to the top of the head and sew along the other side. Sew on the back body piece in the same manner.
Next, have the wearer try on the costume and carefully mark where to cut the face and armholes. Have them take it off and cut those holes. Try it back on to adjust.
Hem at the bottom and insert elastic to gather it into a bubble shape.