Part 1: Once eaten, twice shy
The abandoned warehouse waited in the dark, a defect neon flashing as if it wanted to say "I'm a trap!" "Pshaw, what a hackneyed scene..." murmured Persephone Washington, private dick. No, make that eye. "Good that I'm as black as the night, so two of us can play hide-and-seek."
Then all lights went on. "Now guess what, it was a trap!" giggled the voice of Don Olestra, head of the local mob. "Normally I would be pleased to talk with you about my masterplan of crime until some divine intervention would save your pretty ass, but I'm invited to a dinner party. Hasta la vista, baby!" He waved with his hand, and a machine gun barfed. Persephone didn't even had the chance for a tacky comment like See you in Hades, she fell on the spot. The henchmen carried her away. "Drop her on the next trashheap", ordered the Don.
"I'm baaaaad!" Persephone thought as she awakened in the companionship of radioactive waste, giant rats and chemical leakouts. She wasn't completely dead, which was an astounding achievement given that she had more holes than your standard crime story plot. Fat chance. She felt no pain, the surest sign that she wouldn't see next daylight. She tried to move, but that subsystem had already bitten the dust terminally. And then, from the rest of an eye, she saw it.
It was a common slime mold, genus Myxomycetes. Well, not entirely common. It was a really pissed-off slime mold who had enough of that above mentioned radioactive waste, giant rats and chemical leakouts and had mutated beyond all recognition. A real mothafucka slime mold, if you can apply that adverb to a nonsexual species. Angered about the new distraction, it slimed itself over Persephone (a normal Myxomycetes is pretty fast for his size, so don't wonder about the abilities of a mutant mothafucka Myxomycetes - now say this thrice fast). It came a-sliming through all her holes (both natural and additional) and began to eat (or better: merge with) her cell by cell. Persephone tried to cry her brain out, but that failed due to lack of organ (not brain but lung - it's logical that even a mutated mold needs some time to eat through solid bone). As the mold began to eat private eye private parts, the screwed-up nervous system of Persephone produced an neverending orgasm. Small happinesses was her last thought before everything blacked out.
Well, the end result was a dead private eye and a stuffed mold anyway.
Was it?
It wasn't. (I know that blaming everything on radioactive waste, giant rats and chemical leakouts is bad style, but you accept that silly technobabble in your run-of-the-mill Star Trek story, don't you? Simon says: "I'm the author!") OK, so the result was a dead private eye and an alive slime mold with its identity taken over by the soul of Persephone Washington. "Aw shit", she thought (or should I say holistically-sensed, as there was no brain to think with?) as she regained consciousness and tried to get used to her new body.

Part 2: The sweet taste of vengeance
I tell ya, it was no easy task for Persephone Washington to re-shape into a more befitting form. One day a nubile young black woman, the other a puddle. Ch-ch-changes, as David Bowie sang. But the organizing abilities of the Myxomycetes are astounding, and with the help from some leftover DNA from her old body she turned a bit more solid. A whole year passed until she mastered her new body, but then she was a full-fledged shape-shifter, able to turn into anything. "Odo, eat your heart out!" she smirked and finally left the trashheap to kick some ass.
"Have we ever met before? I don't think so, sweet lady." It was no problem for her to meet Don Olestra at a party and enlure him with a nice body, and the old sack already began to slime at her. Well, she would slime back soon!
"My name is...Myxina," she whispered and throwed some eyes at him (uh folks, that phrase was purely literally).
"OK, let's quit the sugartalking. You want my money, and I want your body. Isn't it so?" That was the only good side of the Don, he didn't drift around a theme for long. "Oh...I'm very...engulfing. Can you satisfy my hunger, Don Viagra?" she teased him. "Gangwayyyyy!" he cried, threw her over his shoulder and carried her into the sleeping room, where he ripped her clothes off.
"Don't exasperate yourself before time!" The lust-crazed Don threw her on the bed and impaled her with his boner, and he surely would have hurt any ordinary woman this way.
"Talk dirty to me, bitch!" "Oh yessss...Vagina Dentata!" "What?" "I said Vagina Dentata!" "Huh?" "Let me explain it this way..." Chomp!
The Don cried in panic as Persephone melted around him and turned into a mass of sharp fangs and tentacles. She planned to be a bit sadistic and let him suffer for a while, but then the goons, alerted by the cries, crashed into the scene and the machine guns barfed again. But this time, they couldn't injure her a bit, only the skull of Don Olestra exploded when the bullets hit. "Spoilsports", thought Persephone, and her tentacles leashed out and strangulated the goons in seconds. Persephone formed a gun-like bulge and blew some imaginary smoke from it.
"Make my day, punks! Hmmmm, but what next? Hey, I'm now Myxina, Bad Girl Superheroine! I need a flashy costume now, and a secret identity, and a ghostwriter for silly puns, and a crossover with Vampirella, and..."

The End