Which entity of the Cthulhu Mythos does Mary meet

Question

In the web novel of Shikkoku no Sharnoth -What a Beautiful Tomorrow-, Mary Clarissa Christie encounters an entity in Serranian which seems to have been apart of the plot of the 《Illuminati》, throughout the novel it seems to hint that it is something from the Cthulu Mythos and i am wondering which one, here is the evidence i have gathered

• In Part 2-3 the 《Omnipotent》 man is working on the remains of an Engine Human saying

That would make it possible for an 《Old One》 like this to stick to it.

it explains before this point what the 《Omnipotent》 man is talking about is something he peeled off

Something like water. But it wasn't technically a hydrogen compound. It wasn't a natural substance.

• above is the image from Part 3-1, the huge eye is the entity while the figure just infront of it is Mary, i'm not sure how much this helps in identifying the entity

• in Part 2-6 Marquis Costanzo, the leader of the Illuminati, Mentions that the fake 《Metacreature》 Sebas destroyed, when it recognized Mary's (Objective A) Golden Eye that it changed into a manifestation of Dagon. before this, after it was destroyed it sprayed water on Mary and from then Mary could hear the entity say "Save Me" more often which seems to indicate the fake 《Metacreature》 was linked to the entity which like what the 《Omnipotent》 man found

• M mentions when he becomes surrounded by the 《Illuminati》 that the Green Stones that the Engine Weapons

had killed and trapped the pitiful "spirit of water" in the Aegean Sea

• i'm not sure how much relevance is makes but the entity takes the form of a dog when it flees with Mary

• also the entity is afraid of the King of Sharnoth (who is M) because it think he'll devour it ofcause this could just be the entity having knowledge of M devouring 7 of the 8 《Metacreatures》 that appeared in the Visual Novel however it may be a reference to a Cthulu Mythos entity being afraid of a king

While this question related to a plot of a Japanese Visual Novel (the Web Novel comes with the game but was translated and hosted on the net) which is more suited for the Anime/Manga SE what i am asking is the identification of the entity which Mary encounters and since the web novel and VNDB seems to hint at the Cthulhu Mythos i figured i'd get a better answer here where there has been questions on it (i only know Dagon and Cthulu from Prison of Ice: Call of Cthulu).

Answer 1

I don't think it's ever explicitly named in the webnovel, but it's likely supposed to be a manifestation of Dagon as you originally posted, due to the water motifs. The figures from the Cthulhu mythos that appear in the What a Beautiful series are only loosely based on their namesakes, so it's likely that it is Dagon.

HPL's Dagon was very nebulously described in his own works anyway and it seems to me that most of the Cthulhu mythos that the WAB series draws from is based solely on Lovecraft's own works and not the expanded mythos of other authors who took up the mantle after him. In fact, in Sharnoth they poke a bit of fun at August Derleth, albeit very indirectly, when Angie describes her poor relationship with her family, so that is quite likely the case (or perhaps I'm just reading a bit too far into it).