I agree that the Newborn really is an absolutely impressive feat, technically speaking (and I'd argue design wise as well, as a repulsive medley of grotesque and strangely sympathetic); the actual animatronic itself is so damn expressive, very unlike anything else we had ever seen in the franchise prior to that point. Thematically, it's the final nail in the coffin, that one last abomination that brings together the "Perfect Organism" and the impurity of human evolution/experimentation. It's a thing that shouldn't exist, and won't for much longer, and that last little 'f**k you' (at least, as far in the timeline as the films have taken us) to humanity's ever-growing attempts to get their hands on this thing.
