The timeline(s) are initially started with the beginning of the original game. A timeline starts the same, but the events happening within the timeline can cause many different routes and endings. In the timeline, there can be many little things that can affect the overall outcome. In the case of Glitchtale, Frisk destroys the Reset button, and that caused the timeline to not be able to end. The game got corrupted forever.
In addition, another thing that can affect the outcome is outside intervention, shown in the case of Yet Darker. Gaster is able to take control of Sans' teleport and take Frisk to his location. That has an impact on the timeline, even though nothing changed with the protagonist.
In Glitchtale, the timeline has become glitched, hence the name of the series, Glitchtale. This causes different paths to be available, such as the revival of Gaster, and Asriel's return. The glitches in Glitchtale occurred because of the random resets in the middle of the timeline that shouldn't be possible.
|“||We can't just... reset timelines like that. It might have side effects on the things we don't want to happen. Imagine it as a matter of probabilities, the more we screw around with the timelines... the more are the chances of bad things to happen. Things that aren't supposed to be here will appear.||„|
|~ Sans on *Determination|
This principle can affect timelines even if events in the timeline are the same to another one. As such, one can be viewing a timeline and not be realize they are just viewing the copy of another timeline.
Resets are the main way to start, or end a timeline. The reset erases most information stored in a SAVE file, such as the user's LV and EXP; resetting, however, does not erase certain variables such as the file name. Similarly to loading a SAVE, some characters will act differently after a reset. A true reset is slightly different though.
While different from a regular reset, it's essentially the same thing, with the exception that the characters will forget anything they would other wise remember from a normal reset, this includes the protagonist themselves as well.
Save Points are not shown to be present in Season 2 of Glitchtale due to the RESET button being broken by Frisk which in return broke the SAVE function, but they are somewhat present in Season 1 as seen with Chara saving. Saves keep the progress of the one who holds the most determination in a timeline. Should they die, they'll respawn from the most recent save point they attended to. Saves reset when one presses the reset button.
Pre-Human Monster War
- Copper and Agate are born.
- Asgore befriends Shane Goldburn and Roy Goldburn.
- An unknown event occurs where Asgore loses his friendship with the Goldburns.
Human Monster War
- The Great Human and Monster Wars happens.
- The seven human wizards meet, and seal the monsters underground.
Post-Human Monster War
- Amber Lightvale is born.
- The current leaders disappear.
- As a result thereof, Copper Lightvale and Agate Lightvale become the new rulers of the kingdom.
- Copper and Agate have an argument which leads to Agate leaving the kingdom.
- Copper and Agate battle again. This time, Agate is victorious and she slays Copper.
- Agate creates Bete Noire before dying.
Unknown time prior to Glitchtale
- Asgore kills 5 humans in the time he has been trapped underground.
- 20 years prior to Glitchtale: Alina falls into the underground and is slain by Asgore.
- Flowey gets a hold of the 6 Human’s determination and tries to commit genocide on monster-kind, only to be continually stopped by Sans.
Frisk falls to the underground, Frisk completes all of the different endings except Genocide Route.
Out of boredom, Frisk attempts to do a Genocide Run on Hard Mode. In this timeline, Frisk is unable to defeat Sans. Chara eventually takes over while blinded by HATE. When Sans was about to get killed by Chara, Frisk takes a hit from them to save Sans. Sans absorbed Frisk's Soul and killed Chara. Sans then resets the timeline.
In repentance after what happened in the last timeline, Frisk decides to do a Pacifist run. Sans teleports both him and Frisk to Grillby's for food but Frisk is lost along the way. Frisk ends up in the Void, where Gaster is. Gaster tries to take Frisk's soul to regain a living status but Sans appears before he can do so. However, Gaster is still strong enough to take Frisk's soul. Sans absorbs Frisk's soul once more and kills Gaster. Sans then resets the timeline.
The Glitchtale timeline starts from Episode 3 of Season 1, the past timelines got reset and no one remembers them except for a few characters, namely Sans. This timeline also sets into motion the build up of corruption and glitches.
In timeline one, the gets corrupted due to the fact breaking of the reset button and Frisk’s manipulation of the save file. As a result, the game created a "checksum", a Bete Noire. A checksum is a concept in programming where there is a command that checks if things are normal, and if not, fixes it. The game was never meant to go past at the end of the Pacifist Run. As a checksum, the game created Bete Noire to set the game back to normal. She was made explicitly to destroy anything, and absolutely everything, and the game could make up whatever backstory necessary to cover it up.
After Frisk erased himself, technically the game doesn’t exist anymore, as in, LV and stats are not a thing anymore. Since Frisk is the player here, aside from erasing themselves from existence ending the glitch that could potentially erase the timeline, he also made sure that the “game” wasn’t in charge of what happened to the timeline either. The only thing that still attaches the world to function as a game right now is Bete Noire since she was created with the purpose to cause a game over screen and fix the mess in the timeline.
The Timeline 1 got erased due to Chara dying, he managed to enter an old-point in the timeline and leave the locket from his timeline there for Asriel to take, with hopes that might be a turning point in the future, changing the outcome and therefore creating “Timeline 2” which will be the entirety of Season 2.Timeline 1 and Timeline 2 is the exact same, but that doesn't mean people died differently.
Timeline 1 and Timeline 2 are exactly the same up to the point where Chara fights Asriel, except that in Timeline 2, there are 2 lockets instead of 1. From now on, everything is new and a new outcome is yet to be discovered.
- In Game Over Part 1, Chara got killed. However, using his determination, he entered into an old-point in the timeline. This got resulted in a split in timelines, in which one may continue while the other is to be erased as a whole.
- This narration is played after the deletion of the first timeline. Because of this, the second timeline wouldn't be named "Timeline2.file" because "Timeline1.file" no longer exists. Because Undertale only has one existing save file at any given point, "Timeline2.file" should be impossible. The timeline shouldn't "play" until/unless it is renamed to "Timeline1.file"
- Glitchtale can't have a reset.
- The second timeline that Chara made was the last hope they had for a successful timeline (which is Season 2). The first timeline was doomed from the very start, and if whatever change they made to it doesn’t work, it’s over for everyone.
- In both corrupted timelines, neither the interface, buttons or LV count.
- There is no way to change the way those functions work and pass it onto other characters other than the player. By ending his life he also took the one thing that tied the game’s rules to the real world. That means Frisk's abilities to manipulating the timelines aren't transferred to Chara.
- The timeline being glitched and messed up was a result of Frisk triggering Hard Mode.
- Hard mode allowed the game to go even farther.
- There was no genocide route in the Glitchtale Timeline.
- ↑ The game got corrupted forever. (Link)
- ↑ Frisk has completed all of the different endings except Genocide Route. (Link)
- ↑ Bete Noire is the game's checksum (Link)
- ↑ Timeline 1 and Timeline 2 is the exact same, but that doesn't mean people died differently.
- ↑ 
- ↑ Glitchtale can't have a reset. (Link)
- ↑ The timeline 2 that Chara made was the last hope he had for a successful timeline (which is Season 2), the timeline 1 was doomed from the very start, and if whatever change he made to it doesn’t work that’s it for everyone. (Link)
- ↑ In both corrupted timelines, neither the interface, buttons or LV count. (Link)
- ↑ There are no way to change the way those functions work and pass it onto other characters other than the player. By ending his life he also took the one thing that tied the game’s rules to the real world. That means Frisk's abilities to manipulating the timelines isn't transferred to Chara. (Link)
- ↑ Hard mode allowed the game to go even farther. (Link)
- ↑ There was no genocide route in the Glitchtale Timeline. (Link)