Fionna decided to take a rest after filling herself with already two monster girls, feeling all their power run through her veins, feeling powerful really turned her on and decided to give herself a private and pleasurable time, but before she could start she heard a very small footprints above her, like it was walking needless. The creature revealed her appearance going down slowly with a thread attached to the ceiling, a beautiful woman that her waist down was entirely the body of a black spider with a red skull printed on her spider abdomen and pedipalps in her crotch, the woman decided to talk exposing the fangs in her mouth and the 8 eyes in her face.
"Hmmm? What am I seeing? This prey is quite interesting~" the spider girl said in a sensual tone as her mouth watered.
"I think you're confused about who is the prey" Fionna yelled to the spider swinging in her thread while using all her arm pairs to grab her four breasted chest.
"Watch your tone~ if you're generous I can give you a quick but pleasurable death~"
The spider almost instantly shoot a web to Fionna and used the thread to throw her on one of her spider nets, leaving Fiona with no movement as she was glued to the net, watching the spider approach to her.
"Don't worry sweetie~ when you notice you'll be dead" the spider covered Fiona's body with spiderweb from her tail to her neck, then opened her mouth with her steamy breath.
Fiona transformed her own arms into vines and used to to scape from the cobweb coverage, then she covered the spider's body with her vines.
"W-what is this!?" The spider yelled.
"See how the roles changed!" Fionna laughed, "I always loved spider's abilities" she brought closed the spider to one of her big mouth.
"N-no! What kind of freak are you!" The spider kept screaming and covered Fiona's three mouths with spiderwebs, "eat me now!" She laughed.
Without noticing, Fionna opened her wide and big snake's vagina and started the swallow the spider, at this point her prey could do nothing but scream and shoot her webs without thinking, with the time the spider was just another simple dish to the mutated scientist.
Fionna removed the web from her mouths and didn't wait to change her body, growing many spider legs in each side of her snake tail, at the end of the tail a small hole opened to shoot webs as a skull printed in the tail, equal to the deceased spider had in her abdomen but black instead of red, two pedipalps grew below her cocks, protecting her vagina and 6 eyes added to each one of her three faces for the final touches. Fiona used her new spider limbs to walk on the spider web and shoot a thread to the ground to walk on it. Admiring the powerful monster she turned into, she was stunned by her beauty but without distracting her from her next goal.