Sandmännchen is some obscure German character from a some obscure children's education show. His greatest apsiration is to become an internet meme, in the vein of the grue, Jesus, O RLY, and others. Sandmännchen is also famous for using his mind control song, which goes like this:
"Unser Sandmännchen, Das Sandmännchen, Abendgruß, Sandmann, Sandmännchen!"
Can you even pronounce this?!? Probably not.