I borrowed the Troll idea from this awesome website! We were a big hit (it was just a tad cold though). We bought long sleeve leotards and tights (nude) from a Discount Dance store, got the colored hair spray and elf ears from a Halloween store, and the jewel is made from glitter foam from hobby lobby. We couldn’t get the jewel to stick very well so we used a small piece of craft wire to secure it (be careful not to scratch or poke yourself).
For the hair: We put a cup on our heads, put our heads upside down and secured hair around cup with a hair tie. Spray away with hairspray and then color with colored hair spray. To get the bright blue I first sprayed my hair with WHITE colored hairspray and then the BLUE. Thanks for the Treasure Troll Costume idea!