Slender Man

Slender Man is one of the secondary antagonists of the original Littlest Pet Shop Fan-Fiction series. He was an unseen villain at first, but as things came closer, he was revealed and seen through some episodes and unseen in others still. He is one of the first creations of Black Soldier.

The Original Creepy-pasta
In his story, he was seen by a girl who was in the woods and as the girl came closer (not Blythe), he stabbed her 19 times. As soon as he did that, he walked to find new victims to murder before any victim finds his eight pages.

Littlest Pet Shop: The Fan-Fiction Series
He was first mentiones by Sunil who thinks he's real. When Sunil starts having a nightmare about him, he gets scared out of his wits. When the pets realize that Slender Man is indeed real, they all become frightened as they were when Jeff the Killer is around.

Quotes

 * "My eight pages..." (His main quote)
 * "What's the last thing you expect me to do?" (Slender Man to the pets)
 * "I am going to murder you... In you sleep!" (Slender Man pretending to be Freddy Krueger)
 * "I love my tentacles."
 * "I'll soon catch all of you dumb cowards." (Slender Man to Roger Baxter, Ms. Twombly, Blythe, her human and pet friends.)
 * "You can run. But you can't hide." (His popular quote)