This is hardly a missable as it can be at any point by just AFKing in the shadows for a minute.
This is another easy achievement to get at any time, I don’t suggest doing this during your Shadow master run.
Climb up the stairs to get the candy
At the blue van, turn left, on top of the red barrel, pick up the inhaler.
During the night breaks between chapter 1-2 and chapter 2-3, go to the front of the truck to show your Mom one of your collectibles.
Inside the green tent, pick up the magazine.
Inside the white tent, pick up the weird plushie.
When chasing the dog inside the warehouse, turn a corner to find the toilet paper in the shopping cart
You’ll soon find the dog, from now on you can pet him 5 times with “E” and throw the ball with “Space.
Climb up on the shelf from the right, pick up the puck.
Hard to miss, pick up the chalk before going down the ladder.
You’ll now have all the collectibles.
Before starting this run, to ensure getting Shadow master, it’s recommended to delete the save files at C:\Users\%username%\AppData\Local\Helpless\Saved -thanks Therzuzada!
This isn’t a hard achievement, take your time to move between shadows and it’s easily doable. This achievement only unlocks on the Survivor mode.
Thanks to FrozenShiver for his great guide, all credit to his effort. you can also read the original guide from Steam Community. enjoy the game.