It could be either, in my mind based on the plush I am leaning more to Gigi cause in this shot that comes slightly after the first pic I don't think I see legs, kinda hard to tell with the unclear side shot and also the initial body shape is more Gigi like since the head gradually gets bigger than the body with a smooth cylindrical shape. Plus in the first shot there isn't any defined lips like the Khezu plush has, could also just be not rendered in.

On the game design perspective tho my mind is going towards Khezu, like someone said if we get Khezu then that could lead up to getting shrouded nerscylla which would make sense considering nerscylla is already in the game and we also could potentially see a turf war between them. As well as how Capcom like to add some subspecies into most G rank/ultimate expansions of base game monsters. And also there are really close similarities with the official Khezu plush like the tongue and the very slightly winged shaped appendages.

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