Scratch

In Sburb, a Scratch is a phenomenon that occurs in certain sessions. Essentially, it is a mechanism by which a session, and the universe tied to it, can be reset to an indeterminate point in the past. The process releases a great deal of temporal energy, and the universe will then redevelop differently and eventually produce new Sburb sessions possibly very different from the one in which the Scratch was initiated. It is a last resort for a session doomed to failure, with the intention being to attempt to restart with more favourable conditions.

One of the most notable effects of the Scratch is that the new session exchanges the roles of the Scratched session's players with their ectobiological parents; this has occurred in both of the known sessions. When the original troll session was doomed to failure, its players Scratched it, resulting in a new session in which they became the ancestors of the twelve player trolls who, in the original session, were their ancestors. Similarly, the kids' Scratch has put their ectobiological parents (Nanna, Grandpa, Bro and Mom) in their places as the players Jane Crocker, Jake English, D??? Strider, and R??? Lalonde. The Hero of Time in each session is given a device to activate a Scratch, although it is rarely used – both the troll ancestors' session and the kids' session are "unusual" in this respect (among many others). In the kids' session, the device the Medium has produced for activating the Scratch is the Beat Mesa in the Land of Heat and Clockwork. The mesa must be scratched (literally) with a very sharp needle to activate the process.

The kids activated their Scratch as part of their plan to get rid of Jack, devised with the help of the trolls. Karkat's first (from his perspective) conversation with John heavily implied that the kids and trolls would meet in person after the Scratch; Rose and Dave have arrived in proximity to Aradia and Sollux, and will presumably meet the other remaining trolls when they arrive, but it remains to be seen whether John and Jade – last seen breaking through the fourth wall – will meet the trolls.

The trolls can't see the future of the kids after the Scratch, possibly because the kids' entire incipisphere ceases to exist. They initially believe that the Scratch is responsible for opening the hole in spacetime that led to The Great Undoing – the arrival of Jack Noir – leading to them calling it "The Rift;" however it was revealed that Jack was fleeing from the Red Miles on Earth (not realising at the time that they were his own doing from hours later). Aradia implies that Jack flees the kids' session to avoid being wiped from existence; the kids have all avoided this fate as well: John and Jade by breaking through the fourth wall, and Rose and Dave by being far out in the Furthest Ring.

voluntarily provides information on the Scratch, as it is apparently part of his plans, but mentions that the mysterious rift in spacetime that happens afterward is "none of his business."

Etymology
The phrase "to start from scratch" refers to the act of starting something over, from the beginning, where an initial attempt has failed and the following attempt is made with nothing carried forward from the first. It originated in the late 1800s in reference to the boundary or starting line of a sports game, which was often physically scratched into the ground.

The Scratch may also be thought of as analogous to a record scratch, a destructive sound produced when a record is forced to run backwards and then continue forwards from an earlier point.

In billiards, a "scratch" is a term for a foul, most often for the act of pocketing the cue ball. After a scratch, the cue ball has to be "reset" to its starting position. While scratching is to be avoided most of the time, there are HS 4503 (scenari0s) f0r which it might be prudent t0 d0 s0. However, a player that scratches while pocketing the 8-ball immediately loses. The trolls' universe was destroyed when Spades Slick "pocketed the 8-ball" (killed ), which was synchronised, in The Tumor, with the kids' universe being destroyed by Jack Noir after he was forced out of their session by the Scratch. In other words, the 8-ball was pocketed while scratching, and both universes "lost".