Gaster is a cat confirmed (kinda)
Ok, so I'll go ahead and come out as a massive Gaster stannie. (My beloved. He barely exists in-universe, but he is so real to me. Pets him on his bald head)
Anyway, there's a small passage in the Valentine's newsletter that caught my eye:
Putting aside interchangeable faces - this is a reference to Alice in Wonderland. Specifically to how Alice plays with verbiage. The notion that words, indeed, mean anything is constantly toyed with (and discarded) in the book.
We're now given this image of Gaster as someone for whom reality is so warped, that words (and perhaps the objects they signify as well) lose concrete shape. It ties in neatly with his use of a font where every letter is a symbol upon itself. The guy sure has a strained relationship with language. (Relatable.)
Of course, this isn't the only Alice reference we have:
So the "friend" is an obvious nod to the Cheshire Cat. This character is known for vanishing, leaving behind only its grin, and being cryptic. Vanishing and cryptic? Sounds familiar.
We have known for a while that the "cat" element exists in DR:
The other elemental pairs - Thunder/Light, Dark/Star - have a throughline of meaning that ties them together. They are things that co-occur with one another. Where there's thunder, there must have been light(ning). Stars can only be seen in the dark. So what's the deal with Puppet/Cat?...
Let's assume "cat" stands for Cheshire Cat-like qualities. Ephemeral, inscrutable, with a tinge of eerie omniscience. Why is it paired with "puppet"? A puppet is something that is, well, puppeteered. It is something immutably material, with no agency of its own. Quite the opposite of "ephemeral and omniscient"!.. Except when you realize that in DR, transcending what you know of reality will inevitably lead to the conclusion that you are...
One is intrinsically tied to another!
The characters in DR who seem to have the most forbidden knowledge have a relation to puppets and/or cats:
(Assuming that Jevil has some jack-in-the-box in him.)
These folks also have ties to Gaster and his juicy knowledge. It is not too far-fetched to assume Gaster himself has Puppet/Cat vibes. In fact, I think that he is the Cheshire Cat of Deltarune. Perhaps he doesn't mind his condition as much as we think!
TL;DR when Gaster is revealed as a catboy, the fandom will implode. Consider this your warning.