This game has hidden developer credits.
Secret Programmer Credits
There are four secret programmer credit messages in the game. Each are written on a piece of paper that appears after you beat all enemies inside a cave or hidden doorway at a particular room in Level 7 (levels 1 to 6 must be beaten first in order to access it). Here is the complete list of these messages and the ways to access them. The first message is located in an open cave and may be accessed instantly. The other three messages are found via bombing a particular spot to reveal a hidden doorway. Once you reveal the doorway clearing the room out within will provide you with the paper holding the secret programmer credit message.
Just open the cave, beat all enemies, and then grab the paper.
Bomb the upper right corner of the room.
Bomb the right section of the room in the middle.
Bomb along the left side wall of the room.