I used this pic for all the characters I made:
White Fleece works well for the beard and eyebrows, but you'll need some sturdy material for the other face pieces. I used vinyl, but you could also use posterboard.
Cut out the face piece as shown.
Before you cut the eye holes, hold it up to the wearer's face and mark where to cut.
Lay the face piece on top of your fleece and cut out the beard. Cut out some eyebrows from the scraps.
Cut out a frowny mouth and pointy teeth.
Cut a crown and 3 red gemstones.
Apply a generous amount of fabric or tacky glue to the back of the mouth and face pieces and attach them to the beard. Do the face first, then lift the nose and insert the mouth underneath.
Glue on the eyebrows and teeth.
Glue the gems on your crown. On the back of the crown, I glued on a thick fusible stabilizer to reinforce the points and make them stand up. You could also use cardboard.
Attach the crown to the face with glue or a sewing machine straight stitch. Measure around the head and secure with a straight stitch or heavy duty glue.
With a sharpie, draw lines on the gemstones and under the eyes.
For the robe, I got a blue graduation gown at the thrift store. To keep the beard in place, I used glue dots on the shoulders.
My husband found it difficult to see while trick-or-treating in the dark, so he simply turned the crown around and wore it backwards. (Also a good tip if you want to drink at a party.)
For Princess Bubblegum, I made a crown out of the same vinyl I used for the Ice King's crown and added a green "gemstone" (cut from an old shower curtain). I reinforced it on the back so it would stand up.
For the outfit, I bought a pink shirt and skirt at the thrift store and made a purple sash to go around the waist. For the hair, I bought a Rapunzel wig and sprayed it hot pink with temporary hair color (which rubs off on anything that touches it).
Whew! That was quite a labor of Halloween costume family love.