More frightening than any ghoulish fiend is what’s festering in our landfills. So think green this Halloween. For alternatives to eco-evil costumes, log on to greenhalloween.org. Some of the “eek-o-friendly” ideas: Dress as a tree, butterfly or cloud (wear all white; cut old bedsheets into strips and tie them to the arms of a shirt so they wave in the wind). Do research on endangered species and dress your child as one she’d like to save. Create costumes using stuff you have around the house, or reuse old costumes by organizing a swap on your block. For a goodie bag, use something you own that goes with the costume; a chef can carry a bowl, a mountain climber a backpack. Your kids will be doing their part to raise eco-awareness one doorbell at a time. Now that’s a treat.