Board Thread:Questions and Answers/@comment-28067574-20160629072532/@comment-27701762-20160629080229

As counters:

1) While I see the vague similarity you are pointing too, this doesn't seem like a suitable premise for two reasons. First, we would then need to claim that any two or more characters that share any vague similarity are in fact the same character: Papyrus/Sans; Toriel/Asgore/Asriel, etc., etc. Second, the similarity only exists at a very particular moment, while at all other times Chara looks like a happy child. If Chara is Gaster, why represent himself/themself in this weird light.

2) Again, this seems like a premise that makes more problems than it solves, since the only tie is the mere act of creation. By the same token, Chara must also be Alphys (who creates weapons and a robot to impress Asgore) and Papyrus (who creates puzzles).

3) We only know that Chara's body is absent from the coffin, and that is accounted for, as Toriel removed Chara's body and buried it in the ruins. The soul, meanwhile, was absorbed by Asriel, and most likely vanished along with Asriel's soul. Chara is probably a ghost who is listening, but that doesn't get us to the conclusion that Chara is Gaster.

What is more, Gaster's disappearance is described as him being scattered across space and time. In contrast, Chara describes their own disappearance as being dead, and that they were awakened from death by Frisk/the player. Given Chara's description, and the fact that they would then have died upon Asriel's death, making Chara Gaster wouldn't fit within the timeline.

4) This doesn't really seem to fit. If we assume that Chara was not evil before the end of the Genocide route, then Gaster's message, which was supposed to have been written a long time ago, doesn't work within the timeline. Likewise, this entry would thus be Gaster describing himself, which doesn't seem to make any particular sense. And finally, the entry continues by talking about shadows and photons, which would signal actual light, rather than evil.

5) I see why you might make this claim, but "man" and "woman" are commonly used to describe monsters as well within the game, and not just humans. The River Person themself, who is a monster (since they would not be allowed to reside in the Underground if they were human), introduces themself by saying "I'm the River Man...or am I the River Woman?"

Likewise, Chara's gender is specifically designed to be ambiguous, since characters refer to Chara as "they" throughout the game. Using this line as proof would cut against that design, meaning that it is a much more likely explanation that Gaster and Chara are distinct characters, than that Toby messed up something so important.