The Unibō enemies bear a striking resemblance to Gordo enemies from the Kirby series.
"HAPPY" is spelled out in stars in the first Space Zone level. However, it's too far up for the player to see it under normal gameplay. Jumping from a specific spot in the level will allow them to reach the letter 'Y'.
In the Pumpkin Zone, there's an enemy called J Son that walks like a Goomba but instead carries a hockey mask with a dagger stuck in it. This is a reference to the main antagonist of Friday The 13th, Jason Voorhees.
The famous "Totaka's Song" can be heard if you get a game over and wait for about 2-3 minutes.
There is a glitch that's caused by going down a pipe, pausing the game, and exiting the level with Select. When Mario enters any level, he'll go through the floor as if he was still going down the pipe.