The Cougar Boy is basically a very horrible and stupidly named Gameboy clone.
It’s pretty rare, especially stateside but not exactly in high demand. In South America (primarily Brazil), it was sold as the “Cougar Boy”. While in in France, the Netherlands, and Germany it was sold as the “Mega Duck”.
The cartridges are very similar to the ones of the Watara Supervision, but slightly narrower with fewer contacts.
Link (Thanks K!)