It adds upgrades.
They took Nidhogg, made it a separate creature with new abilities (like you did with the Punisher), took the texture (or rather, the image) of the Abyssal Serpent's dwelling, and placed it after building the Dracolich. As a result, both are available in the building window, but they are different creatures. Is it possible to do this in Heroes of Might and Magic III?
И пусть Эльрат осветит твой путь