Some of the runthrough videos you can buy with the Star Coins end up being this. For example, 1-3 has Mario and the Toads using Yoshis to relay Luigi across the level to get easy 1Ups.
Playing the game with multiple people quickly becomes this, especially if you can round up a full 4.
The first battle with Iggy in World 5.
Bowser Jr. getting left behind in Worlds 4 and 6 and discovering his father's Koopa Clown Car and subsequently kicking away his own, still battle-damaged from previous bouts with Mario. Also, the castle falling on Bowser at the very end.
From the ending, Luigi falling down when attempting to lean on the gondola of a balloon that had already taken off.