Romeo used the Go-Slow Ray in an attempt to slow down the city, and ultimately the whole world. The PJ Masks were hit by the ray and were slowed, but they still managed to win against Romeo by dropping the Ray from the building's roof in the city square, thus destroying it and shutting it down.
Owlette's New Move
The Go-Slow Ray was among the multiple inventions which Romeo repaired and improved in another attempt to take over the world. This time, the ray was placed on Romeo's Robot itself. The Robot could fire the beams through his 'eyes'.