My question was specifically about movie contents. However, I have to acknowledge that difference about the games themselves should also be discussed, so here you go.
I'll premise that last year I've gone through a period during which I myself also used to be in favor of having separate branches between Blue/Red and Yellow TASes, as I expressed in
these posts. However, I was aware that my opinion was partially biased, which is the reason why I decided to not judge TiKevin's first
Yellow "game end glitch" submission (AKA NSC). And in light of that audience reception and Memory's
overview, I couldn't disagree with the decision of obsoleting the previous
Blue "warp glitch" publication.
Now, getting back to this submission. You say that Blue/Red and Yellow presents a slightly different storyline with different challenges and opponents, but I'm not sure how much you mean with the term "slightly". For me there needs to be heavy and obvious differences scattered through most of the run, in order to warrant a separate branch, like it can be seen between Ruby/Sapphire and Emerald. So let's take a look at Pokémon Yellow and see what did it introduce compared to its predecessors, along with my remarks:
- Instead of choosing a starter, you get a Pikachu, while your rival gets an Eevee.
Seeing this game difference displayed on the cover of the game, some people could feel that it's major, but if we look at a typical full run, it's actually not, may it be a speedrun or a casual play. The player is not forced to use Pikachu for progressing through the fights. Actually, the game is pretty much forcing you to pick a different Pokémon soon, otherwise the Brock fight is almost impossible. And on the other hand, you're soon going to get all the traditional starters you want, so it really doesn't affect the game challenge much in the end.
- Some mandatory battles are different, including: rival fights, 6 gym leaders, and some Team Rocket.
Even if some Pokémon used by these trainers are different, the Parties end up being overall similar to the ones featured in Blue/Red, so from the perspective of casual gaming, the challenge and the gaming experience is almost the same. The only exception are the last 4 gym leaders, that feature clearly higher levels. Still, the Elite Four parties are the very same. The final fight with the rival features different Pokémon, but these are still covering all the major types, and the overall levels are still there.
- Minor differences in game behaviors.
As I said, we can't consider few minor game mechanics as worthy of a separate branch. In fact, we don't allow separate branches for each revision or localization of each game. We still have to consider each on a case-by-case basis.
For the sake of argument, let's have a look to an example for which I instead consider separate branches to be good: Pokémon Ruby/Sapphire and Emerald. I took my time watching the current glitchless TASes of
Ruby and
Emerald respectively, and I easily noticed many game differences through the whole of each movie:
- In Emerald there are some different and some additional mandatory events and battles, most notably around the awakening of Groudon and Kyogre, which is the main reason why the relative TAS is about 40% longer.
- Many trainers and gym leaders used different Pokémon through the whole run.
- There are many differences in routing, more than the route differences between Blue/Red and Yellow.
- Emerald re-implemented a phone functionality that allows to have rematches with many trainers, including all gym leaders. This also introduced some new mandatory dialogues.
- The game interface and features of Emerald are updated with the looks and functionalities of Pokémon FireRed/LeafGreen, which makes it feel a bit more modern.
Now, getting back to Yellow, let's take a look at how many things are the same as Blue/Red:
- Almost all fights with common trainers are unchanged.
- All events are unchanged. (except getting your starter/s)
- Doesn't introduce any difference in maps. (except for Cerulean Cave, which was also different for Japan Green/Red; in any case, it's not visited in glitchless run)
- Doesn't introduce any new or different game feature. (except talking to Pikachu and the Pikachu Surf minigame)
Also note that it doesn't help that Nidoking was used for both movies. But more than that, it doesn't help that the current
Yellow labelless publication has an average rating of just 6.6, while there are 2 other active branches with higher ratings for
Yellow alone; 4 branches if we also count
Blue and
Red, for a grand total of 5. Accepting this submission as a separate branch would mean to end up with 6 separate branches for Gen I in total, which would be way too much in my opinion, even if the ratings were better. And I'm not even counting the
Blue & Red coop diploma.
Lastly, as a side node, I want to add that Yellow is not that much original as a game. Some people may think that it's inspired to the
Pokémon anime, but if you look at that anime closer, you will see that Yellow is just
faintly hinting to it. You get a Pikachu as a starter and you can walk and talk to it, and that's it. The rest isn't even that accurate to the anime. Oak doesn't catch Pikachu in front of Ash. Gary doesn't steal Eevee before Ash could grab it. And the traditional starters Bulbasaur, Charmander, and Squirtle, are just given away to you without showing much plot behind it at all. Then you fight Jessy and James just 4 times through the whole game (3 if you use Poké Doll on Marowak's ghost), while instead in the anime they appear every single day, often fighting with unlikely giant robots, making it a ripoff of
Yatterman.
There is really nothing else that makes Yellow's plot unique. Just for making an example: the anime featured more than
60 original characters just for the Kanto saga, and guess how many of these were included in Yellow? Zero.
