Specifically in regards to Shyren’s sister, it does seems strange that she “fell down” long before the experiments began, yet she is still used in the True Lab experiments. However, it is never clarified exactly how long the state of “fallen down” lasts, only that it leads to the monster’s death. It’s possible that this extended state of “fallen down” is not abnormal.
Entry Number 6 states the following: “Their bodies came in today. They’re still comatose…
And soon, they’ll all turn into dust.” It seems likely that a monster who has “fallen down” is not unlike a human in a coma. While technically still alive, they are unconscious and unresponsive. A human coma can last anywhere from a few hours to several years. If this is the same for monsters, it would explain the time discrepancy with Shyren’s sister.
What is known about Shyren’s sister is that she “fell down” before Mettaton gets his body.
After this first entry, the diary entries mention that Mettaton’s cousin becomes a training dummy, Mettaton meets Alphys, and Alphys shares her sketches for Mettaton’s new body. Alphys then presumably makes Mettaton his body and uses the success of her project to become the new Royal Scientist. All this time, Shyren’s sister would have been in a state of “fallen down.”
BRATTY AND CATTY: So, like, I’m pretty sure she… Made Mettaton to, like, totally impress [ASGORE]. A robot with a SOUL… That’s, like, SUPER relevant to his hobbies! So after seeing Mettaton, ASGORE… Asked her to do all this science stuff for him! But nobody’s, like, seen anything from her yet. Or… her at all… She must, like, just stay in her lab all day.
The reason no one has seen Alphys after she built Mettaton is because she was busy with the soul and vessel experiments, which went horribly wrong. Since then, she’s been spending all her time in the lab and garbage dump.
While this seems like an unreasonable amount of time for Shyren’s sister to remain in a “fallen down” state, it is still not enough to support the idea that her body was collected by Gaster. In fact, Gaster starting the experiments makes even less sense with what is known about the gap between him and Alphys. After Gaster was “shattered across time and space,” “ASGORE waited so long to hire a new Royal Scientist.” This time disaprity is mentioned by two of Gaster’s followers.
If the determination experiments were taking place during Gaster’s time as the Royal Scientist, it would not make sense for Asgore to wait a long time to replace Gaster, especially when the monsters’ bodies may soon turn to dust. Also, keep in mind that Alphys is mentioned as being a faster worker than Gaster.
It may be that Alphys’ work on Mettaton’s body took a much shorter time than one may expect, meaning that Shyren’s sister may not have been in a state of “fallen down” for an exorbitant amount of time.
What we do know about Gaster is that he was the royal scientist, he created the core, and he fell into his “creation.” If Alphys’ actions were attributed to Gaster because he was shattered across time and space, any of the events in Undertale could be attributed to him in this manner. However, it is very unlikely that Gaster is related to the experiments that resulted in the amalgamates and Flowey.
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read more: Alphys wrote the True Lab Entries.
Beyond the evidence, it also makes sense to consider this thematically. Alphys is wracked with guilt over her experiments. From reading her journal entries in the True Lab, it becomes apparent she is in way over her head. Frantically injecting determination into everything and getting zero initial results, the tone of the entries becomes increasingly erratic.
Through the efforts of Frisk and Undyne, Alphys is eventually able to come to terms with herself and confront her past. If Gaster truly created Flowey and the Amalgamates, it completely invalidates the story of her transformation. From a thematic perspective, Alphys’ redemption arc is rendered meaningless if she was never responsible for things going wrong.
TL:DR Alphys is a brilliant scientist and also a bit of a disaster and nobody can take either of these things from her.
honestly just really like undertale 