Golden Egg #3 is located on level 3-2 of Angry Birds Seasons Trick or Treat. Break the floating pumpkin with a reverse shot using the Boomerang Bird. This one is pretty nifty, so check out the video if you are having trouble.
To obtain the star on the level, simply fire the Red bird into the pile of TNT immediately in front of the slingshot. This Rube Goldberg machine is pretty consistent, so no worries here.