Jonny Quest vs. the Cyber Insects/WMG
This Dr. Zin is the clone from the end of Jonny's Golden Quest.
Like his Replicants, he is either physically degenerating, or the only part of the fatal disease the original Zin managed to cure with the cloning process was the respiratory illness, explaining why he looks physically wasted like the original Zin, but doesn't need the oxygen bottle. The disease is still killing the clone, though, and is affecting his mind in particular, which explains his irrational behavior such as killing his henchmen for trivial reasons and his sudden mood swings.
Dr. Eve Belage is actually an environmental extremist.
Okay, so belage's E.D.E.N. project is dedicated to cloning extinct wildlife, but she also clones and preserves what appear to be thousands of prehistoric assassin bugs. Dr. Zin calls them "the most rapacious insect known to man" and even Belage admits as much when trying to dissuade him from turning them into his Assassinoids. When pressed as to why she was cloning them when she knew how dangerous they were, Belage's only answer is "To help people, Zin!" But what could can such destructive and dangerous prehistoric insects serve? What is Belage's definition of "help?" This troper suspects that this, combined with her E.D.E.N. project aboard Quest Station (an ark type biosphere) has a little bit of Utopia Justifies the Means to it, and that Belage was planning to wipe out all life on Earth with the cloned assassin bugs and then replenish it with the animals she and Mylana had aboard Quest Station. It goes without saying that Dr. Quest was unaware of any of this, nor were there any official files, otherwise Zin would've seen them when he had the reprogrammed 4-DAC transfer all of Quest Station's files to his computer. Belage's indignation at Zin creating the Assassinoids? She was just peeved Zin stole her idea. Her insisting on keeping the frozen piece of Assassinoid at the end suggests this plan is still a go, just slightly modified to employ Zin's own Assassinoids instead of the regular ones.
Race was Faking the Dead.
Race's Disney Death was intentional on his part. Sick and tired of Jonny's attitude problem, and particularly pissed off that the kid took them headlong into a pack of enemy ships, Race feigned death after being only mildly injured by the exploding control panel. With his pulse slowed enough, the three kids, being untrained medical professionals, naturally assumed he was dead. He did this in order to teach Jonny that his impulsive actions have consequences, figuring that the emotional distress it would cause his daughter would be worth it just to get Jonny to start acting rationally. And it worked.