Doomed timelines

Doomed timelines are a phenomenon in Sburb based on the fact that many events are the result of closed time loops. A doomed timeline is created when a person fails to do what they are supposed to do causing the entire timeline and its inhabitants to be doomed. Interaction between doomed timelines and other universes is prevented; however a person can travel back in time from the doomed timeline and avert the timeline ever being created. In fact this is at times necessary to succeed, meaning a doomed timeline has to exist in order to ensure its own non-existence. Players from doomed timelines can can also send their memories back to their past selves on the alpha timeline. This is accomplished by going to sleep before the doomed timeline is erased. It is possible because, according to Dave, dream selves operate somewhat outside the normal time continuum, allowing memories from alternate timelines to be passed on.

Players that die in doomed timelines can appear in Dream Bubbles within the Furthest Ring. Doomed players who enter the alpha timeline also appear in dream bubbles after they die. Players that are still alive when a doomed timeline is erased do not seem to enter dream bubbles, as they cease to exist.

Kids' session
There have been 3 doomed timelines in the Kids' session. The first brief one is where the Draconian Dignitary didn't receive any resistance to the theft of Rose's Journals, resulting in Dave traveling back and to prevent him from stealing them in the Alpha timeline. This attempt failed, but the corpse of his alternate self made Dave realize that he could not go back in time and prevent the theft.

The second and most important one was created when John, under the guidance of Terezi, prematurely met Typheus and was killed by him. This would have various effects, such as John no longer being able to perform the ectobiology needed to create him, his friends and their guardians or allow Jade entry into the Incipisphere. This would also mean Becquerel would not be prototyped meaning Jack Noir would not become a threat to the trolls which would lead to them not trolling the kids thus not tricking John into prematurely meeting with Typheus. Alternate Future Dave originated from this timeline and prototyped himself, believing that the kernelsprite's preference for dead or doomed things would save him from death. Additionally, the Rose of this timeline was able to transfer her memories to her alpha timeline self, causing the awakening of her dream self.

The third doomed timeline was also created under the guidance of Terezi. Through a coin flip, she guided a past Dave off course in order to demonstrate to present Dave how to attain the God tiers. She gave present Dave the choice of killing his alternate past self on his Quest Bed, allowing that self to reach God Tier. However, present Dave was unable to kill his alternate past self, doomed or not. The doomed Dave was later killed by Jack Noir.

Trolls' session
The Trolls' session was plagued with at least a thousand doomed timelines, HS 5904 (many of which) Karkat blames himself for. However the army of Aradiabots produced by these ended up being critical in the fight against the Black King.

Interestingly, part of the genetic code found in First Guardians that was needed to create came from a doomed timeline. In this doomed timeline, created when Karkat did not run the Mobius Double Reacharound Virus, Gamzee killed all of the trolls and wrote his part of the code in Karkat's ~ATH manual. The Aradia from that timeline brought the book back with her and somehow ensured the version from the alpha timeline would be destroyed in the explosion of Karkat's computer. The alternate timeline version of the book was later stolen by Agents of Derse to create.

Another doomed timeline seen was the result of Terezi being unable to bring herself to kill Vriska. In this timeline, Terezi allowed Vriska to leave the troll's meteor to fight Jack Noir. However, Vriska left a scent trail from her wings, allowing Jack to find the meteor and kill the other trolls. When he had accomplished this, he returned to fight Vriska. The outcome of their battle is unknown, though has stated he wouldn't bet against Vriska winning (were he a gambling man). This timeline was envisioned using Seer powers and Cue Ball-granted omniscience, and so may have only been a potential timeline as opposed to an actual doomed timeline. Aranea HS 6672 (implied) that this may not be the case, however, as she knows about it and that Terezi caused it but is not a Seer.

While traveling through The Furthest Ring, the characters on the meteor encounter other trolls that died in doomed timelines. Some of these trolls had attained God Tier before they died, including an alternate Feferi, an alternate Eridan, an alternate Tavros, and an alternate Karkat.

Pre-scratch Trolls' session
While the pre-scratch troll session has never been seen revealed that the events that lead to them scratching their session was HS 5953 (not simple inadequacy but rather more comprehensive and systemic), including a failure to perform the ectobiology needed to create themselves meaning their entire timeline may have been doomed. claims this is a subtle glitch that exists in some sessions that are destined to be scratched and is in fact the calling card of. On the other hand, it's possible that this merely created an unwinnable null session, rather than an actual doomed timeline.