Galactic Pinball

Here's an interesting Metroid cameo. Galactic Pinball, Samus Mini-game: Hit the ball into the top-right part of the Cosmic board with the bumpers. Start the "Bumper Clash" sequence and hit all the bumpers to start a Samus mini-game. The S symbol from Super Metroid will appear in place of the bumpers, and the phrase "Let's Go, Samus" will be spoken. The ball will transform into the Samus' ship, with the goal of shooting Metroids and other targets while the Super Metroid theme is played. Thanks to Ferry Groenendijk of Virtual-Boy.net for this description and the screenshots.
-Samus Pinball
-Another screenshot.

Mario Clash

During the bonus game in MC, Luigi, Princess (behind the flag on the left),Yoshi (not pictured), and a lot of mushroom people can be seen sitting in the crowd. Yoshi is on the right side of the stands. Thanks to Ferry Groenendijk of Virtual-Boy.net for this screenshot.
-Mario Clash bonus