There are 50 collectibles in the Xbox 360 version of this game. This is a list of all of the collectibles for the sake of simplicity including the letters.
None of the following video guides are mine. So thank the people that made these amazing youtube video guides.
Here is a condensed video with all 50 collectibles shown. Thanks
Deranged Asylum !
Some of the videos below do not have all the collectibles shown in the individual videos (but the ones that do not show up should have descriptions that should make it easy to find) and the Homestead video below is more of a lets play than a collectible guide so the video guide above is definitely worth checking out!
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Prologue:
1. Missing poster
2. Letter 1
3. Thank You Note
4. Fridge List
5. Beth Hayes Wake Pamphlet
6. Letter 2
7. Crumpled Note
8. Letter 3
9. Arson Article
10. Charlie’s Drawing 1
11. Framed Matheson Farm Picture
12. Charles Note 1
13. Construction Article
14. He Came For Me Notebook (aka the collectible that ends the level)
The collectibles that video won't show:
7. Crumpled Note is found in Kate's room behind the trash can after using the key to open the door for storyline progression. Before the slide collectible in the video.
10. Charlie Drawing 1 is located behind the burned down Matheson's house in the prologue, propped up against the backdoor, half buried, near the painting collectible (11). It is kind of hard to see unless you know it was there.
Eight Pages:
15. Oakside Park Sign
16. Oakside Park Rules
17. Oakside Park Pamphlet
Into the Abyss:
18. Letter 4
19. Letter 5
20. Closing Note
21. Letter 6
22. Charles Note 2
23. Warning Note
24. Letter 7
25. Mine Article
Flashback:
26. Letter 8
27. Letter 9
28. Letter 10
29. I Want to Die Note
30. Letter 11
31. Homestead Note
31. The video doesn't show it as its newly released for this current Slender the Arrival version. Luckily, you can't miss it. its right underneath the video tape for Homestead.
Memories:
None
Escape:
None
The Arrival:
32. Letter 12
33. Historic Kullman Mines sign
34. Letter 13
35. I'm Sorry Note
36. EPWS Note
37. Letter ?
38. Charles Note 3
33. At the 28 second mark on that video, that rock to the right has a plaque on it that blends in due to the bad coloring in the game. (in my opinion). New collectible.
36. Not in the video but immediately after the fire forest, when you enter the building. Immediately left on the wall. (just before finding the key). Thanks to Jumbl3dPr0 for clearly reminding me and Deranged Asylum for pointing me in the right direction to remembering it.
Homestead:
39. Maggie Letter
40. Charlie Drawing 2
41. Granary Reminder
42. Granny Richter Volume
43. Charlie Drawing 3
44. Matheson Family Picture
45. Frieda Note
46. Walter Picture
47. Verzweiflung Illustration
48. Rose Diary
49. Maggie Diary
50. Franziska Letter
39. 1:36 (in the house on the table)
40. 2:35 (in the barn, ground floor next to the stairs)
41. 3:26 (in the entrance of the silo on the wall, can't really miss it)
42. Not in the video, in the cellar, in one of the rooms on the bottom shelf next to the colored drawings on the wall. Its easier to find than it sounds.
43. 8:00-8:40 (in the back of silo of collectible 40)
44. 9:00-9:06 (in the shed near the key in the backyard behind the silo)
45. 11:39-11:42 (in the chapel on the table to the left)
46. 11:59 (in the front of the chapel on the table to the left)
47,48,49,50. 13:15 - 13:57 (all on the 2nd floor of the starting house)
Genesis:
None
And that's all of the collectibles! Happy hunting.