Dr. Elrod Purvis is a biochemist working as an assistant to Dr. N. Zyme at Megakat Biochemical Labs. He's a greedy S.O.B., and takes issue with his boss' desire to give their latest invention away to the city. In an effort to solve hunger and deforestation, the two scientists developed Viper Mutagen 360, an experimental formula using snake DNA, that revives dead cells, and the idea is you pour this green goo onto dead plants and they come back to life. They test it out on a flower and it comes back to life.
But while as mentioned the philanthropic Zyme is planning to donate the Viper Mutagen to Megakat City, his assistant Purvis has other ideas. "This formula could be worth millions to the right bidder!" he plots evilly.
That night, he turns down going home with Zyme to return to the lab under some pretense or other, intending to just walk out with Zyme's notes and a jar containing the mutagen. Easy as pie! Unfortunately, as fate would have it, Zyme forgot his reading glasses. Returning, he catches Purvis with his hand in the cookie jar and demands an explanation.
Purvis could try and think up some lie. Who knows? Maybe Zyme will buy that Purvis is merely moving the sample and the notes to a more secure location than "out where anyone can take them from the unlocked main lab."
Alas, being a villain in a kids' show, he immediately goes into evil mode, declares his intent to rob Zyme, and runs off. Zyme pursues him. In the stairwell there's no sign of the culprit, but it turns out he's just hiding behind the door.
There's a fistfight on the stairs that Purvis wins by knocking Zyme down the stairs, and he rushes down the stairs past his stunned employer. Not about to let his treacherous assistant escape, Zyme kicks his briefcase down at him. Struck, Purvis pitches forwards and crashes violently offscreen.
It's then revealed he spilled the mutagen all over himself. He promptly dies.
A while later, as his body is being carried off on a stretcher, Zyme explains to Commander Feral of the Enforcers that the mutagen caused some kind of shock to Purvis' system and killed him. And because he's a nice guy, he actually sounds sad about it.
"It wasn't your fault, Dr. Zyme," Feral reassures the scientist. "His own greed did him in."
Cut to the morgue sometime later. Purvis' body lies on a slab covered by a sheet, complete with a toe tag. Suddenly, it begins twitching. Beneath the sheet, changes are taking place. Not only is Purvis coming back to life, he's transforming into... something else. And judging by the reaction of the hapless attendent who wanders in just as this ghastly resurrection is happening, it ain't pretty.
The mutated Purvis retraces his steps to Megakat Biochemical through the sewer, sneaking in past the elderly security guard who's too busy with his nose in a comic book to notice the mutant waltzing into the building. Upstairs, Zyme is gathering things up in preparation for a presentation to Mayor Manx and still lamenting Purvis' death when he notices the flower they'd tested the Viper Mutagen on earlier has mutated to grow fangs and a forked snake tongue. Oops. It seems the mutagen is horrifically flawed and therefore worthless for anything good.
A disappointed Zyme makes to call Manx and tell him not to bother coming, when a voice hisses from the shadows: "You won't be telling Manx anything, Zyme!"
"Who's there?" Zyme asks. "Is that--Is that you, Purvis?"
"Not anymore...!" hisses a half cat, half snake figure that emerges from the darkness. "Jussst call me Viper. Doctor Viper."
And with an evil cackle, the resurrected Purvis, now the fiendish Dr. Viper, begins his campaign to doom Megakat City to a neverending strain of hackneyed mad scientist plots, starting with attempting to transform Zyme, Manx and Callie Briggs into cat-snakes like himself. As you do.