SPOILER ALERT: This contains an easter egg. If you want to look at this stuff yourself, go back. OK, so I've been playing Super Mario Galaxy 2 for a while, and I've got to the Shiverburn galaxy. Well, yeah, since it was new level, I did some exploring. Opon my exploring, I found something-- something very unusual to find in a Mario game. There was these three things looking at Mario. I used first-person mode and looked to the left from the begining of the stage to see it.

OK, now, I was pretty creeped out now. I did some researching and found several sources that had the explanation. Someone digged deeper into it and found this:

It seems that these alien creatures were designed for a beta level that was scraped in development, called BeyondHellValley. The file for the weird creature picture came out as HellValleySkyTree. It may be a designed for a creature/object in the level. I'm guessing the level was scraped since the game was aimed at younger audiences. And that's not all. Whenever you look to the left from there, you will see these as if they are actually following Mario. We guess this was an easter egg that Nintendo left in there. But these are still interesting to ponder; WHY do they follow Mario if all coding was deleted? We assume that it was left in by a mistake. They do not look like they actually moved from the spot, because it's in order. Big, medium, small. And there's the fact that NOBODY in the game has said anything about them.Even if the game is hacked, you STILL can't get to them. They are textured to always be at a distance Mario cannot get to. Also, there are easter eggs in Super Mario 3D land that may be relevant to this. I don't know which level you can see this in, but if you use the binoculars to find a Toad, you can zoom up a little bit. Wait a minute, then a UFO will be seen. This may be a reference to either the easter egg in Mario Galaxy 2, or the UFOs that can be seen in FaceRaiders. And also, you can see a gjost (not a Boo) if you go to the Ghost House at world 4-4. Finish the level, and go to the end of the stage. Go past the FlagPole, and you'll be infront of the wall. Jump up on the fence part, and wait about 1 minute to 30 seconds, and there will be a ghost. It stays for at leats 5 sconds, then it will go away. This stuff REALLY creeped me and my brother out, and I wanted to see if anyone knew too.