Mario Fortress Galaxy - A callback to Mario Zone from Super Mario Land 2, One of the stars involves you piloting Mario Zone like a mech and fighting off Mecha Bowser. You also encounter Mini Marios from the Mario vs. Donkey Kong series as NPCs.
Pinball Mayhem Galaxy - Basically one of those...
The cutscene right before the final phase of the final boss fight in TTYD.
The ending of Sunshine when...
The opening of Galaxy.
The ending of the first Mario vs. Donkey Kong where...
Wario and Waluigi's shenanigans during both the openings of Mario Power Tennis and Mario Golf: Toadstool...