Yeah what I meant was more along the lines of how you'd imagine the character to die if the story was real, y' know? Of course he simply gets damage and dies in the games logic
But if you think about what feeling you'd like the Slenderman to convey, it will help you choose an appropriate sound. If he's supposed to be more of a ghost-like entity that messes with your mind, you'd go for surreal, maybe static sounds (like in the original Slender Game), if he kills people by destroying their bodies, you'd go for bone-cracking sounds or flesh ripping apart, that sort of thing... you get the idea ^^
Personally I think you should maybe choose something that isn't too reminiscent of the original Slender Game (those static "white noise" sound effects) so your game stands out more in comparison and gets its own identity...
As for the music, I quite like it, but I think it is too "melodious" to be used as ambient music. I don't know the correct terms to describe it, but it sounds too much like an actual song instead of an ambient track. It would be good for special scenes (Like in one special story-relevant room or maybe during a cutscene) but I think you'll still need to find something that is better suited for just playing in the background and creating atmosphere.