Doctor Man and Him Being Human
In Bioman I guess some people already figured out he was human (while maybe believing the Big Three were cyborgs, not full robots). Now it was this revelation in Bioman that didn't really linger until the finale but was revealed mid-season.
In Bioman episode 19, we get the first hint that Doctor Man was a Japanese scientist and a human being. How? In the beginning after Mason intended to probably blow up the Biomen while releasing some explosive gas into the air, Prince arrives. Prince declares himself to be Dr. Man's son after Mason threw Mettzler's fencer towards him, which the scratch made him look like he was human. Well, Dr. Man then introduces the Prince to the Big Three as his son and heir, which Mason thinks, "I didn't know Dr. Man was a human." and Dr. Man's deteriorating condition showed he was really human. When Mason saw Prince design his own robot, he exclaimed that Prince is truly Dr. Man's son being able to build a robot his age. However he didn't know at that time that Prince was a robot. But strangely Mason didn't immediately plan to get rid of Doctor Man, maybe because he had to formulate a plan to do so. I was pretty surprised to find out that the Prince was actually a robot replica of Doctor Man's real son. Phew, I was glad that the Prince wasn't really Doctor Man's son or it'd be a waste of his youth. However the whole plot about him and his real son Shuichi played a much bigger part towards the near finale.
After the destruction of Doctor Man's artificial son, we see Doctor Man's lungs were starting to deteriorate and Mason mentioning, "I never expected Doctor Man to be a human and to be at this state." So yeah, Doctor Man was deteriorating and he is seen repairing his cybernetic parts. He wants to live longer. Mason doubts his creator since he always thought Doctor man was a robot.
In Bioman episodes 25-26 we see Dr. Man's real origins. So why didn't Mason plot Dr. Man's supposed downfall earlier than that? I mean, Dr. Man already revealed that if the boy was really his son (Shuichi) then there is that birth mark then that is a hint he is human. Hmmm I guess Dr. Man may have mind wiped the Big Three several times or they just later malfunctioned. In Bioman 28, Mason led a failed conspiracy to kill Dr. Man and to let the Big Three rule since they thought that Gear should be ruled only by robots and not by a human being. Yet Dr. Man fooled them with a mechaclone decoy. Dr. Man ended up countering their threat and reprogramming the Big Three to serve him to the very end after he had previously remade himself into a full robot. However despite his remodeling, Dr. Man still had a heart left in him as in the finale, he finally granted his son's last request before he died.