The Halloween Run takes place in Lassay-les-Châteaux, Mayenne, on October 31. This festive, non-competitive event is organized by the association Le son de vie and does not record finishing times. The route is approximately 8 km, though the distance may vary, and participants have 1 hour 30 minutes to finish. Starts are divided into waves, with a maximum of 200 people per wave.
Costumes are required, and headlamps are necessary as the run occurs after dark. The course has led participants through streets, a garage, and a castle, contributing to a Halloween night outing atmosphere rather than a typical road race. Past participants have worn costumes such as vampires, butchers, and killers, and one edition saw 450 runners participate across three starts.