The transfixatron was a device built by the Constructicons under the direction of Megatron. It was a projectile device that fired energy bursts that could nullify a Transformer's transformation process. (This would later be mimicked by another device in the future.)
Generation One cartoon
When the Autobots undertook a motor race for charity, Megatron used the opportunity to use the transfixatron on the Autobots while they were in vehicular mode. While the Autobots were racing, Skywarp teleported from a remote location to the air above the Autobots and successfully fired the transfixatron on the racing Autobots. Skywarp was called "Delightfully treacherous" by Megatron for his actions.
Bumblebee, Ratchet, Wheeljack, and Huffer managed to escape the transfixatron because they chose not to participate in the race. These Autobots, with the help of Spike and Chip Chase, managed to develop a grenade that could counteract the effects of the transfixatron, which was ultimately destroyed, but not before being used against Devastator, causing him to dismantle...for some reason.