He is tall, has yellow horns, and has wavy hair.
By acts like he is helping the children from the Goosebumps HorrorLand books. In reality though, he actually works for The Menace and gets the kids interested in escaping from HorrorLand to go to a "safer place" called Panic Park.
He tricks the Very Special Guests into thinking that Panic Park is the safe place and HorrorLand is the dangerous place. Actually, the truth is the opposite. Byron uses mirrors to suck the children into Panic Park, a place completely grey-scale, with scarier rides and even scarier shadow people. The Shadows can surround themselves around a child, and make them become invisible.
Byron is eventually revealed to be working for The Menace as he brings out the Fear Meter. The Menace wants all of the children's fears to get up to 100 so he can bring Panic Park back from 1974 into the modern-day.