Singularity

This time it is a Metroid easter egg hidden deep within the hold of the Pearl. During the Central Docks stage, inside the Pearl, there will be a room with a Dethex grenade launcher and a door that you cannot open. Through the window you will see a Weapon Upgrade case, taunting you from its position of safety. To the right of the door, you will see a habitrail-style passage behind a mesh grating, starting with a small opening at the lower right and winding it's way up the wall. Using the alternate fire, send your Hamsterball of Doom into the opening, and use the button to jump it to the platform on the right. Jump back and forth up the passage, until you can move to the left and maneuver it down into a passage under the floor. Roll it around until it passes under the locked door and comes to a stop, then release to blow open the door. Enter the room and look at the far wall to see the Ambassador from Zebes (who is completely tanked), and read the nearby note for a Morph Ball joke.