The below description is taken from LEGO.com.
Who is this masked avenger of the night? It’s Bartman, the mysterious four-and-a-half-foot crime fighter who guards Springfield’s streets. No one is beyond the reach of his trusty slingshot, be they supervillains or tin cans placed on fenceposts. Very few know (or care) that Bartman is secretly none other than Bart Simpson, wearing a homemade costume. But hey, every show needs a superhero, and this is the best we’ve got!