Dr. Robotnik's Mean Bean Machine
"Dr. Robotnik's Mean Bean Machine" for Genesis is a "Puyo Puyo" clone. It's just "Puyo Puyo" with a Sonic skin on it.
Included in many Genesis collections, I spent a lot of time in college playing this late at night with some buddies. We used to run tournaments for this game and it was so much fun.
So "Puyo Puyo" is similar to "Tetris" in that you're moving blocks around in order to clear some lines. Where it differs is that you're trying to match colors in a group of four or more. By setting up chains, you can send over "garbage Puyo" to your opponent so that they're unable to clear some of their Puyo.
It's a great little head-to-head tetris-like game and matches can get super heated if both players know what they're doing. The story mode for "Dr. Robotnik's Mean Bean Machine" isn't anything special, but it doesn't need to be, it's Puyo!