If you have a party store near you,you can check to see if they have anything Muppet themed. As for the cake,or cupcakes,try the local bakery(usually in supermarket bakeries they have muppet themed cakes,I know mine did when I worked in it).Or if you are doing the cupcakes yourself,how about decorating with the number 16 in some nice colors &/or candy. Some suggestions could be allowing your guests to come dressed up as their favorite Muppet character. If you'd like also,have a sing-a-long with Muppet songs only(maybe do a Muppet karaoke).Maybe a game of Muppet quotes or perhaps a drawing game like Win,Lose or Draw(Pictionary) where you draw a Muppet,or something Muppet themed(you would have to make categories) & 2 teams,everyone takes turns guessing what you are drawing.Or Muppet charades,acting out something Muppety.Or if you're really creative,make some Muppet shaped pinatas & fill them with candy & muppety type goodies.Decoration ideas,hmmm... How about some neat Muppety colors for the streamers.One wall can have a rainbow(for Rainbow Connection),another with green & orange,yellow & red(or other muppety colors). Happy sweet 16th(for next year)!! Gosh,that was so long ago for me.