And it has been explained online that the giant form of Alien Ghose was also supposed to emerge in the episode along with the normally human-sized aliens and Pandon.
Meanwhile, the Tokusatsu Hiho magazine with tribute articles to the designer Noriyoshi Ikeya showed the design of Giant Alien Ghose drawn by Ikeya back then among the representative monsters he designed.
To me, this is definitely the first time I have seen it, but, according to the Hiho article, surprisingly enough, Giant Alien Ghose was not included even in the script with no plan at all to make it appear in the episode.
It seems that Ikeya himself described it in his art book as the alien he designed with a western armor in mind having something in common with the aliens he also designed for “Silver Kamen” in later years without referring to any other details about the character.
Therefore this leaves it unknown why Ikeya designed this giant version of the alien regrettably.
The dark-colored alien design with no features on its face and nothing outstanding makes the character look very much creepy deserving the name of Ghose that came from ghost though it surely looks attractive in its own way.
I think it is an excellent job with much of an Ikeya feel to it, and it is also impressive to find he designed it as the giant version has nothing in common with the human-sized form.
Incidentally Pandon is the monster remodeled from his original design, and, if you are interested, see this post.