"I arrived at Blackwood Manor one cold Saturday morning amidst a thick veil of fog, the weather didn't look good and there was an unnatural calm surrounding the area. Yet... I soon became entangled with the place..."
Chekhov's Gun: Almost anything that looks peculiar, or seemingly useless item collected, or object you can interact with in the first minutes, you can bet it will play a major part much later.
Chekhov's Skill: Michael's secretary, Barbara, mentions that she's been studying languages in her spare time. This becomes useful when Michael reveals a letter in Italian and sends it to Barbara for translating it.
Haunted Castle: Blackwood Manor. Possibly subverted according to what was found on Last Visit.
Hearing Voices: Early on in the game, there are the eponymous scratching noises. Later on the main character starts hearing whispering voices (that might or might not be real) mocking him during the exorcism of the cursed mask.
James Blackwood also heard whisperings coming from the mask's room, Christopher Milton in his diary questions his sanity when he also mentions hearing them.
In-Universe Game Clock: The grandfather's clock in the entrance, which serves as an indicator of progress since it advances only when a puzzle is completed; And certain events can only be completed at certain times.
It's for a Book: Michael tries to get information from the retired police-officer William Bailey by pretending to be a reporter writing about famous murder cases.
Ironic Nursery Tune: First with the music box hidden in the attic, then on the nursery and near the ending.
Karmic Death: Christopher Milton's fate at the end of Last Visit.
Maybe Magic, Maybe Mundane: The game never actually shows whether there were really any supernatural events in mansion or if everything was only a series of unfortunate events that Blackwood in madness blamed to a curse. Last Visit at the end gives a rational explanation for everything but the final coda hints that there's still a missing piece and something doesn't fit...
Multiple Endings: There's a secret ending that appears only if you perform certain tasks in a certain order.
The secret ending is unlocked by being a diligent writer. Going to Michael's typewriter and writing a page of his novel until it has finished gives you a story in which Michael has not experienced anything paranormal - he's gone mad, like James Blackwood before him.
And it explains just who was in the first casket of the crypt: Milton.
Scenery Porn: Seriously, exploring Blackwood Manor is akin to visiting a virtual art museum.
Screw This, I'm Outta Here!: Subverted, Michael fixes his car and attempts to leave the mansion on the third day, but he doesn't because he fears that something terrible might happen to someone in the future, so he decides to stay until he solves the mystery.
Self-Deprecation: Arthate's working notes for his book, in which he can't decide if a supernatural force is responsible for the scary events or not, and points out the flaws in choosing either alternative. The game itself seesaws between supernatural or natural explanations, and ends ambiguously.
Sequence Breaking: Even if you correctly guess Robin's name and use it to open the box in the study, you will still be forced to go through the puzzle in the crypt to try and find it.
The back cover of Arthate's first book is a Shout-Out to Dark Fall: Light's Out, whose creator Jonathan Boakes worked on Scratches.
The entire process that unlocks the secret ending is a reference to The Shining, as it involves clicking Micheal's typewriter multiple times throughout the game, and each time Micheal says something different, also noted in his diary. Over time, he eventually goes mad, eventually not wanting to look at the typewriter at all and saying in his diary, "I am not Micheal Arthate. He used to be a great writer. But me, I can't write. I am a nobody." Another step requires selecting the responses in the conversation with Chief Bailey that sound more unhinged.
Skepticism Failure: Christopher Milton, but later he starts experiencing the same things James Blackwood did.
Spooky Painting: The painting called The Hands Resist Him AKA The Haunted eBay Painting appears on the second floor near the bathroom.
And it's just one of several.
The Last Visit shows that this hallway full of paintings was robbed of all but one: Chronos eating his children. "Most likely too scary for the burglars to take."
Sundial Waypoint: Twice: Once in the crypt and later when you use the tip of the tower's shadow as a reference to find Catherine Blackwood's tomb.
Surprisingly Similar Stories: The game shares several similarities with 5 Days a Stranger, namely: They are both set on England in a Victorian mansion that the protagonists cannot leave, there is a terrible backstory on the manor's former owners, the games' progress is divided in days, they also involve finding a secret room by looking at the mansion's plans, an African artifact is pinpoined as the source of the curse, theres the action of entering an inaccessible room by rappelling from the outside, and the Madwoman in the Attic trope.
Take That: If Michael inspects the bookshelf in his room, he finds a book of a certain someone whom he seems particular displeased with:
Your Princess Is in Another Castle: The Director's Cut features an additional chapter: Last Visit set after the events of the game. This chapter invalidates the hidden secret ending from the original game.