When I checked, the mask fleetingly appeared at the very end of the ending credits with the director’s name Tsuneo Kobayashi (1911-1991) credited (I know little about him) rather than in the ending scene.
Talking about the story of this episode briefly, it is about a science researcher with a crooked personality who kidnapped boys and demanded ransom under the pseudonym of “Red-eyed Jaguar” to get money for the development of a holographic image device he was working on without being rewarded with any social reputation.
I don’t think this is such an attractive story because it has some unnatural settings I don’t think make sense, but this episode is well known among tokusatsu fans since Ultraseven appeared in it as the “costume” worn by the evil man as a street advertising character handing out toy sunglasses to children at a toy store in preparation for kidnapping the targeted boys.
The body of the Ultraseven suit that appeared in this show seems to have been made from fabric while it is likely that such a suit of Ultraseven was used at stage shows or possibly at other local events as one of the photos covered in an issue of Tokusatsu Hiho magazine shows an Ultraseven costume of the same kind (they may be the same costume).
Although it has no choice but to look cheap, it is impressive to find the Ultraseven mask attached to the suit looks exactly like the real ones used in the series while I assume it must have been cast from the original mold.
The appearance of the Alien Shadow mask at the end of the ending credits was apparently unrelated to the episode story, which makes me guess it should have showed up simply because (the costume of) Ultraseven appeared in the episode (such irrelevances are conspicuous in this episode).
It was fun to find the kidnapped boys’ father was played by Asao Matsumoto (1928-present) known to have impressively acted Ishiguro in Ultraseven episode 2 (he also played Matsui, observatory employee, in Ultraman Episode 8 who was rescued by Pigmon).