Chapter 1: Happy Birthday Slenderman

This is my first fanfiction! I decided it should be about Creepypasta because I've been reading a lot about that lately. This fanfic might be a bit dark. But that's just me. Please review or favourite if you want! It would be much appreciated!
(As a side note, I might review your fanfictions without logging in under the name 'Silver Blaze'. I am just using another device that doesn't let me log in.)
Thanks, Silver Renegade Blaze

Slenderman walked to the door gleefully. Today is going to be a good day, he thought. I'm certain I'll get a victim. Maybe they'll struggle. Makes killing a whole lot more fun when they struggle.
He stopped in his tracks. There was a letter on the doormat. We never get letters. I mean, everyone who lives here are psychotic murderers. Who would send a letter to a bunch of psychotic murderers? And what kind of postman would deliver a letter here?
That was when he remembered his distant cousin, Senderman the postman. A shiver went down his spine as he bent down to pick up the letter. He had a VERY bad feeling about this.
He opened the letter, and a trickle of pink glitter spilled out, followed by a black rose and a headscarf.
Oh no.
He slid the letter out. It read:

Happy 500th Birthday!
The whole family are coming to your mansion for your Birthday! We will be staying overnight for a sleepover!
From Splendorman, Trenderman and Offenderman

"NOOOOOOOO!" yelled Slenderman.
Sally came downstairs, rubbing her eyes and yawning.
"What's the matter, Slender?"
"Oh, nothing, Sally. I'm fine. Go back to bed."
Sally raised an eyebrow.
"Do you really think I'm gonna believe that?"
Slenderman sighed.
"Alright then. My family are coming to a sleepover tomorrow." They heard Jeff laugh from the living room.
"That's not so bad. I'm sure it'll be fine."
Jeff laughed louder.
"They're going to annoy everyone-especially me. We are very different from each other."
"No kidding", said Jeff as he appeared at the doorway. "Hey, everyone, come and hear this!"

The other pastas came into the hallway as Jeff told them what was going on. They all started laughing.
If Slenderman had eyes, he would be glaring by now. But he didn't, so instead, he said, "You know, they WILL mess with all your stuff."
They all stopped laughing.
"My knives!"
"Our cheesecake!"
"My videogames!"
They all ran off to go and protect their stuff.
Sally hesitated.
"Will they mess with my toys?"
Slenderman sighed.
"They might. Go on, quickly, put them out of sight. Then go back to bed, OK?"
Sally went upstairs, glanced behind her for a second, then disappeared to her room.
Slenderman went upstairs, abandoning his plans for a hunt.
After all, it was going to be a long day tomorrow.