The Slenderman Song is a song by ZipZipper, also known as TheIllusoryGentalman (his YouTube channel). It is not sung from the perspective of anyone or thing in particular, it is simply about the Slender Man himself.
Lyrics
Slender Man Slender Man all the children try to run
Slender Man Slender Man to him it's part of the fun
Slender Man Slender Man dressed in darkest suit and tie
Slender Man Slender Man you most certainly will die
Slender Man Slender Man his branching arms are for collecting
Slender Man Slender Man his face is empty of expressing
Slender Man Slender Man he won't let you say goodbye
Slender Man Slender Man you most certainly will die
You most certainly will die (x4)
Slender Man Slender Man sometimes hums a lonely drone
Slender Man Slender Man he will wander around your home
Slender Man Slender Man blends in well within the trees
Slender Man Slender Man in the fog he's hard to see
Slender Man Slender Man dressed in darkest suit and tie
Slender Man Slender Man you
most certainly will die
Slender Man Song