Somerville’s Fluff Fest has turned 20, and all were invited to celebrate the famous treat in Union Square on Saturday, September 20. This year’s milestone theme, Forever Fluff: 20 Years of Sticky, Sweet Somerville, marked two decades of celebrating the invention of Marshmallow Fluff in Union Square with zany games, music, fluff-filled snacks, and more. — Photos by Bobbie Toner