Sega Technical Institute.

Purchased along with our Sega Genesis (a model 2, released in 1993) from Toys R Us. I think it was a pack-in, but there's a chance it was sold separately. As one of my earlier videogames (and having no onboard save), this is one where I played the first few levels over and over.

My earliest memory of playing this game, though, was being in the kids' area at the Incredible Universe electronics store in Wilsonville (which later became a Fry's Electronics) where they had a bunch of game consoles set up to keep kids busy while parents shopped. One of the consoles had Sonic 2 running, and a previous player had managed to get them stuck inside some scenery somewhere in Chemical Plant Zone.