He's a towering hulk of a man in a red boiler suit, black gloves, and a white clown mask. He's white, has short brown hair, and wields a kitchen knife.
He's an escapee of Lincoln State Sanitarium, and invades the home Sarah is babysitting at. He kills Jack with a screwdriver before moving in on Sarah. Sarah manages to gun him down with a revolver, but by the time the authorities arrive, his "corpse" is long gone.
In Sanitarium Massacre, the lore has Burr gunned down by police in a home invasion and locked up in a mental hospital for 8 solid years, before snapping, escaping his cell, and wreaking havoc upon the staff with his trusty handy dandy soulmate-ish butcher's knife. It's very possible that this game serves as a prequel to Babysitter Bloodbath, and that Burr preyed upon Sarah after finishing up the massacre of his hospital.