Things to know for personal reference-
Terezi: Witch of Mind (not blind)
Gamzee: Knight of Rage
Kanaya: Sylph of Space
Aradia: Seer of Time
Vriska: Heir(ess) of Light
Everyone went God Tier before Jack came in and busted the place up.
Disappeared: Feferi, Eridan, Tavros, Karkat, Sollux, Signless and The Handmaid.
Non-existent: Equius and Nepeta, on account of not having those characters.
its hard playing characters that know more than you do about their canon. hard and no one understands
-In the comic it is shown that the codes used to make Doc Scratch were t1ck, t0ck, 8r8k H34DS and honk HONK. Without Tavros the code sequence was never complete (Tavros provided t1ck), which means Doc Scratch has always been incomplete on a genetic level. There was no one to provide the code that the Black Queen stole from the FLARP manuals, so he has always been glitched since existence. Lord English is also glitched to an extent because of this, but the majority of the issues vanished once the BREAK happened so it didn't affect the demon as much as it has Scratch. Scratch's erasure point is before this however, so he is still afflicted with his missing genetic code as a result of Tavros vanishing from history.
Due to this Scratch is going to slowly become sicker over the course of the event and halfway in will begin to detriorate from the inside out and become more sickly to the point of potential hospitilization by the end of the event. His regains will glitch as part of this, as his powers also glitched as a result of the missing codes back in the trollverse.
-As he is coming in early for the erasure canon, he will not be as open to communication with players from the troll session. Due to the lacking cycle of revenge he also never had any contact with Terezi. The only two he will know are Vriska (who he still hasn't realized stole his cueball because Terezi never told him) and Kanaya, who he still raised and awakened on Prospit as she keeps the same role (Sylph of Space).
-Without Handmaid, who we are saying he failed to bring to the moon due to his glitching powers, he took on a more vital role in crafting the hemospectrum and creating bigotry throughout the eras. No noticeable changes came from this, other than being far more callous and more strategic. In other words, he isn't the same "excellent host" he commonly prides himself on and is far more condescending toward the ones he has manipulated (ie the trolls) because of the more active role he took in it.
-As Handmaid was originally supposed to be closer to the concept of death for trolls, as recent updates show, Scratch replacing her means that he becomes more or less characterized as Death and Doom in her place. The lack of his cueball head won't mean much for this, but he certainly will give off a colder air compared to his usual friendly demeanor.
-Also is far more violent, having to take on both his role ("While I am his weapon of subtlety and precision") and her role ("an apparatus of terror and suffering"). He won't hesitate to hurt someone if he is pushed the wrong way or even bothered by them, instead of just brushing them aside as no big deal.
-As a final note to that, he also teamed up with The Condescension a lot earlier. Without Signless to inspire rebellions, it made more sense for him to team up with her sooner than later and get things done ASAP. He gives her a carefree life along with the iron fist, thanks to the hemospectrum he designed, and she works with him. With her acceptance he arranged for the assassination of the current next-in-line (ie he carried out the murder himself) though this heiress wasn't Feferi because she doesn't exist.
-Will frequently look at his scrapbook of panels and try to figure out who all the people in it are, as many of them begin to disappear from his memory. If anyone in 916 Bilko wants to try and find it in the open, as he usually keeps it hidden, they are free to whenever he is too preoccupied to remember to put it away.
-He won't completely forget the original verse, but the moments of recognition and understanding will flicker off and on as the event continues. Right now he hasn't forgotten anything, but will start showing signs quickly. As a note, he'll also know everything about the erasure verse keeping in line with his role as a First Guardian.