@Strym I'll post the corrections for you here, I'm about to edit this again to add information for Frisk in a few mins.
Timelines created from Flowey Here (<- there's a link for this) he stated what he did:
- He burned every book and read every book
- Killed everyone and spared everyone
- Won every game and lost every game
Let's start with the books, there are already 2 possibilties, one where he burns the books and one where he reads the books
Now, about killing everyone and sparing everyone, we haven't found any provided evidence for Flowey doing the Neutral Endings that Frisk did, so we'll lowball and make just 2 possibilities (Pacifist Route and Genocide Route).
Now the games, the most important thing is that there aren't just games with a possibility of winning and a possibility of losing, but there are:
- The Ball Game
- The Quiz Show
- The First Floor Door Puzzle
- The MTT News
- The Third Floor Door Puzzle
Excluding the games that Flowey can't play with as he doesn't have any arms and the games that only Frisk can do, the only possible game he was implied to be involved in are the ones that relates to Papyrus, which he can do and that would be the Ball Game.
There are also 100 possibilities too with the FUN value (<- this one also has a link)
Since Flowey implied that he did any single combination, I assume that he combined all these possibilities together, so I'll multiply all of them.
Total number of possibilities (Without the books):
- (Monster Possibilities) * (Game possibilities) * (FUN value possibilities) = 2 * 8 * 100 = 1,600
1,600 (Total timelines/endings created from a combination of possibilities for PC version-only)
Total number of possibilities (With the books):
- (Book Possibilities) * (Monster Possibilities) * (Game possibilities) * (FUN value possibilities) = 2 * 2 * 8 * 100 = 3,200
3,200 (Total timelines/endings created from a combination of possibilities for PC version-only)
Since we have the PC version, the PS4 & PS Vita version, and the Nintendo Switch Version, due to fundamental differences that these versions have between them, we'll triple the amount:
- 1,600 * 3 = 4,800 (Low-End for all versions)
- 3,200 * 3 = 9,600 (High-End for all versions)
Total number of timelines created from Flowey = 4,800 (Low-End) to 9,600 (High-End) (
2-B)
Copy only the corrections to the Frisk section:
- 4 Hard Mode Endings
- 85 Alternate Neutral Endings (4 of the alternate Endings were already mentioned and the 4 Hard Mode Endings do not include Fun Values)
- Being soulless doubles this amount because you were never originally soulless in these Neutral Endings + you get extra dialogue from Flowey when you're soulless too
- 26 Alternate Timelines created through Frisk's 13 reloads of them reseting the timeline (The process of doing this involves deciding whether to spare or kill Sans due to Sans mentioning that other Sans-es exist, which strongly implies that this was the cause of that)
In total:
- 1 + 3 + 2 + 2 + 3 + (85 × 2) + 1 + 2 + 4 = 188 (Number of Timelines/Endings without including Frisk's 13 reloads of reseting the timeline)
- 188 + 26 = 214 (Total number of timelines/endings without FUN values)
- 210 × 100 (Fun values, changes in each route you do) = 21000 + 4 (Hard Mode doesn't include Fun values, which must be separated from the total) = 21,004
21,004 (Total timelines/endings in the PC Version-only) (
2-B)
Remember, PS4 & PS Vita and Nintendo Switch Version are 2 extra parallel timelines due to the fact as shown in PS4 & PS Vita Version,
this version has the game exclusive Dog Shrine whereas the Nintendo Switch version,
the dog shrine is destroyed and Mad Mew Mew replaces Mad Dummy in the game, so the total number would be tripled but we have to exclude the Dirty Hacker Ending from both the PS4 & PS Vita and Nintendo Switch version as its impossible to get these endings from those platforms.
The total amount for the Nintendo Switch version is the same as the PS4 & PS Vita, so it gets multiplied by 2 and then added to the total of the PC Version.
In total:
- 209 × 100 = 20900 + 4 = 20900
- (20900×2) + 21,004 = 41,800 + 21,004 = 62,804
62,804 = Total timelines/endings from all 3 versions (
2-B)
As for Deltarune, Deltarune is confirmed to be in the same multiverse of Undertale's, and there are 3 SAVE files/timelines in total (
2-C) but however, we don't have direct confirmation that it's part of the Undertale multiverse just yet, so the timeline count from Deltarune remains separate until proven otherwise.
Total number of timelines:
- Flowey's timelines/endings created from a combination of possibilities: 4,800 (Low-End) to 9,600 (High-End)
- Frisk's timelines/endings + other timelines: 62,804
Low-End count:
- Flowey's timelines (4,800) + Frisk timelines/endings & other timelines (62,804) = 4,800 + 62,804 = 67,604 total timelines/endings (2-B)
High-End count:
- Flowey's timelines (9,200) + Frisk timelines/endings & other timelines (62,804) = 9,200 + 62,804 = 72,004 total timelines/endings (2-B)