There is an unused icon of a stack of papers stored in the game's memory.
The enemy "Starfish" is a reference to Starfy of the Legendary Starfy series. The enemy bio states that he is rumored to be a prince of a kingdom, which Starfy is, and all of the Starfish's sprites are Starfy's with sunglasses added on.
There are several test levels left in the game's ROM. In one of them, Iggy Koopa is actually the boss, but due to him having no coding, he dies as soon as you enter his screen.