Shredder wearing the ambulet protecting Humans from the Mesmerizer radiation.
The Mesmerizer is a device invented by Krang in the 1987 TV series episode Super Bebop and Mighty Rocksteady, in his attempt to hypnotize the Human population of New York City.
Bebop and Rocksteady climb the Channel 6 rooftop to place Krang's Mesmerizer atop the broadcaster. Failing, they are temporary replaced with two robots, Mighty Bebop and Super Rocksteady.
Only Humans can be affected by the device, requiring Shredder to wear an amulet to protect himself from the radiation. Once Donatello has knocked the device off him, Shredder believes he is a monkey.
The Mesmerizer is destroyed when falling from the Channel 6 rooftop at the end of the episode.