Heidi Klum’s Halloween costume this year is meant to be petrifying.

On Friday, Ms. Klum, the model and host of “Project Runway,” transformed into Medusa, the powerful monster from Greek mythology said to instantly turn onlookers into stone. (Her husband, the musician Tom Kaulitz, dressed as a warrior turned into stone.)

Every year, Ms. Klum spends months trying to outshine the array of other costumes she has worn to her annual Halloween bash, which has become something of a mainstay in New York City over the last quarter-century. In years past, she has dressed as a worm, a peacock, a werewolf, an ogress and E.T., the endearing alien from Steven Spielberg’s 1982 film. She has also dressed as a “clone” of herself and as an older version of herself.

As Ms. Klum posed before photographers, more than a dozen animatronic snakes seemed to slither from her head, and her eyes glowed with reptilian contact lenses. Her body was encased in a snake suit with a nearly 8-foot tail, which housed a battery pack for the writhing snakes and a set of wheels so she could wriggle around. Her costume made it difficult to sit down and was so large that she took up most of the blue carpet outside the Hard Rock Hotel in midtown Manhattan.