Baddy McBad is a villain who appears in the "Elmo the Musical" segment, "Superhero the Musical."
She claims that she's the baddest of them all and blocks the city playground with a giant boulder. Mighty Elmo is able to move it, but Baddy retaliates using her giant, robot supersuit. She now places a giant anvil in front of the playground, which Mighty Elmo can't move.
Baddy laughs maniacally at her scheme, when her suit topples over and she's unable to get out. She's surprised that Mighty Elmo helps her up despite her bad deeds and the city citizens sing of his kindness. Baddy wants to be just as kind and changes her name to "Goody McGood" and vows to be as kind and helpful as Mighty Elmo.