Slender: The Arrival

In the final chapter, look closely at the messages written in white on the walls of the cave. One of them reads "DONT GIVE HIM TWENTY DOLLARS".

Successfully complete the game under the Hardcore difficulty setting.

Find the slide outside the house during the Prologue, then use it.

Find the radio near the garage in the house during the Prologue. Use the radio a few times until "I Love Radio" is earned.
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The over-sized sign is the entrance sign at the start of the "Eight Pages" level. You should encounter a type of cabin with a few collectibles near it. The sign to earn "I...I'll just...take this..I guess?" should be hung on the wall.

Play the Genesis level under the Hardcore difficulty setting. Run to find the first page, then find the other pages while looking for Slenderman. Once you see him, run to him to die. Collecting more pages while waiting for him will improve the chances of his appearance.

Use the piano found in the house during the Prologue a few times until "Master Pianist" is earned.

During the prologue, go to the slide behind Kate's house. Climb it's steps to reach the wooden fort, then step onto the slide.

Reach the burning forest part of the "Arrival" level. Stop moving and allow Slenderman's tentacles to grow and get you.

When attacked by Slenderman in "The Eight Pages" level, you will not be able to pause game play. Repeatedly press [Pause] under the easy difficulty setting when far enough from Slenderman so that he will not kill you if you are at the limit of the "no-pause zone".