Transparencies, or slides, were frequently used in art departments back in the 90’s before everything became much more reliant on digital mediums.
That’s good for us though, as these outdated items look amazing framed, especially in a light box. Even better, these always seem to sell for relatively cheap.
The seller has several available from the NES era. My favorite? The Bucky O’Hare and Teenage Mutant Ninja Turtles 3 slides. There’s a cool one features Mario bad guys as well.