Monitor
Annoying blue light
The hovering blue light you meet up with in the swamp is the 'Monitor', also known as '343 Guilty Spark'. He's initially friendly, but that doesn't stop him being an irritating pain in the neck, the way he rabbits on like some sort of demented Roddy McDowall. Sadly you can't blow him to pieces, but there's nothing to stop you trying, just to make your feelings clear. He'll object, but he has no weaponry to actually do anything about it.