For Satoshi (Bin) Furuya, the original Ultraman actor, Haruo Nakajima who played Nelonga was a senior fellow as both of them were actors belonging to Toho Company.
The battling scenes with the veteran kaiju actor seems to have been tough and requiring.
Furuya states in his memoir, every time he was asked which kaiju was toughest to beat, he would answer it was Mr. Nakajima.
The mechanism to make the translucent horn glow with a light moving from bottom to top inside was the work of Shigeo Kurakata who was in charge of mechanisms.
He says the antennas which turn forward when emitting electric shock were not his work.
He assumes it was manipulated by piano strings manually on the set.
Tohl Narita stated in his art book that he wanted to make a typical four-footed monster and that he added a pattern of stripes like a tiger to make it look more colorful (photo C).
In a well-known still photo for promotion having Ultraman, Alien Baltan and Nelonga, the suit of Nelonga seems to be unfinished.
It didn’t have the tiger pattern on the back with no antennas on the head yet as shown in photo A, B and D. (In addition, the eyes of Ultraman seem to have no eye holes yet, either.)
Incidentally, Tohl Narita’s art work of Nelonga has no antennas, so they must have been added to the suit just before the shooting.