Feeling accomplished with her acquisitions for the night, Fionna decided to have all four of herselves meet back up at the abandoned mansion so that she could consolidate her new DNA and get some rest. Fortunately, all of her happened to approach the park at roughly the same time, with a few hours left before dawn. However, as she drew near to the mansion, Fionna could hear a rather noisy scuffle going on nearby.
As the four Fionnas came in view of the courtyard outside the mansion, she could see two monster girls fighting each other in the open space, one much larger than the other. The larger woman appeared to be somewhere between a dragon and a lamia, having a wide, draconic lower body with two legs and a very long snake tail trailing behind it. Tracing her gaze upwards from the legs, Fionna saw that the monster girl's body split into five necks, each one ending with the upper body of a woman having six arms. The way that all the women looked the same and fought in sync led her to believe that she was just one woman rather than several conjoined.
Turning her attention to the other combatant, Fionna saw that she appeared to be an ordinary sized woman, with nothing remarkable save for two things: first, she was swinging around a large, dangerous-looking scythe, and second, there was no head atop her shoulders and three identical heads were floating in the air around her. "A dullahan...?" Fionna thought to herself, surprised at the variety of monster girls she had encountered in one night. Sensing that it would likely be a bad idea to be seen by these two aggressive monster girls, Fionna elected to move her bodies into more hidden positions so she could watch the battle and get a better feel for what these two monster girls were capable of.
It appeared that the dullahan kept trying to get in close so she could strike at the draconic girl, but she was having a rough time competing with a quintet of alert gazes. Meanwhile, the larger woman appeared to be spitting up a noxious looking fluid that was visibly corroding the ground wherever it landed, but found her opponent to be too nimble to hit. This exchange maintained a status quo for about five more minutes until the dullahan finally found her opening and managed to land a clean slice through one of the dragon-girl's necks. With a shout, her opponent raise one of her large legs and swatted the headless girl away from her with a powerful blow. Meanwhile, Fionna watched in increasing interest as she saw that the severed neck and torso quickly dried up and turned grey before dissolving to ash. At the same time, the stump of the neck began to vibrate lightly as it started to lengthen and grow back, and soon a crease formed along it as it separated in two. Moments later, both of the quickly growing necks were back to their full length and girth, and a new copy of the woman's torso regrew at the end of each. "A hydra-taur!" Fionna thought in shock, scintillated by the ideas she was getting of what she could accomplish with a body like that.
The fight was not over, however, and the dullahan's movements seemed a bit slower since she was obviously hurting after the last blow she suffered. Just when it looked like she was about to get hit by one of the hydra-girl's acid attacks, the dullahan intercepted it with one of her floating heads. Her other heads clearly winced at the pain of that head being melted away, but then one of them suddenly split into two heads.
Seeing that the two opponents clearly had options to extend their fight for a rather long time, Fionna decided that she had to take action if she wanted to assimilate both girls before one of them permanently snuffed out the other. Quickly formulating a plan, Fionna had her body that was previously in the northern woods use her new kitsune DNA to grow 9 fox tails above her butt, then used her illusion ability to cast a thick fog over the area. Next, she had her body that was by the seashore grow a mass of tentacles around her waist, then sneak up behind the hydra-girl. In tandem, Fionna's body that had been in the back alleys used the oni DNA to bulk up all her arm muscles, and approached the dullahan girl. As the two victims looked around in confusion at the sudden fog, Fionna quickly grabbed the dullahan in a vicegrip while using her hair vines to lasso the floating heads, and began stuffing her body into her mouth while manipulating her hair vines to chuck the floating heads into her fourth and final body's newly created lipples. At the same time, the other Fionna began pulling the hydra-taur by her tail and shoved it into her pussy, pulling her in as quickly as she could muster. As soon as each of the hydra's six torsos looked her way, she quickly fired webbing at their mouths to block them from spitting venom, and swiftly used her new octopus tentacles to grab each torso and suppress the resistance. The plan worked like a charm, and soon not a trace remained of either girl except for the damage caused to the surrounding environment during their scuffle.
With the intruders taken care of, Fionna gradually cleared away some of her fog after she did one more search to make sure there weren't any more uninvited guests around. Gathering in front of the abandoned mansion, Fionna once again turned all four of her bodies into slime, then had them merge together in one big glob. Feeling all of the new DNA settle into a single body, Fionna reshaped herself again before she moved on to incorporate her new changes.
Applying the changes from the red light district first, Fionna chose to grow two new pairs of breasts, then turned the nipples on her lower two pairs into vaginas and the nipples on her upper two pairs into mouths. She then stuck out her long, serpentine tongues, and willed each of them to split into three (for her heads and her breasts). Since she had absorbed no shortage of multi-armed girls, she also decided to double her number of arms from six to twelve. Each arm had the muscle strength possessed by the oni, but still appeared slim and feminine thanks to her slimegirl abilities. To round off the changes, she triplicated her pussy, then grew two more cocks in addition to her existing three and extended all of them out to the same impressive length that the oni had.
Moving onward, Fionna debated with herself over the fact that she could grow a tail that opened like a mouth, a cluster of octopus tentacles, and up to nine fox tails, but felt like all of that would get rather crowded. In an inspired moment, she decided to hybridize all three to conserve space. Concentrating, the chimera woman grew out nine octopus tentacles, but instead of the undersides being coated in suckers, they looked to be fuzzy fox tails instead. Additionally, each of them could open as a large mouth at the end, toothless and containing three tongues inside each of them.
All that remained was to incorporate the dullahan and hydra DNA. Not particularly eager to test the head detachment and multiplication at this particular moment, Fionna contented herself with incorporating the DNA without testing it, feeling assured that she could utilize it later if she so desired. Focusing on the hydra genes, she pictured her upper body splitting in two, and moaned in pleasure as she felt her body diving downwards from the top, starting with her heads. As her two torsos fully separated and reformed into complete copies of the original, Fionna kept the split going until it reached about twenty feet down her greatly lengthened lamia tail. She then repeated the split a few more times until she had five necks and their attached torsos like when she first saw the hydra-girl. Curious as to how it felt to lose a body and regrow it, the scientist summoned the dullahan's scythe in one of her hands, and used it to slice one of her other branches clean off. Surprisingly, she felt nothing beyond an admittedly pleasurable tingling, and basked in the incomparable feeling of having two new torsos grow back.
Ever-curious in nature, Fionna wondered if the feelings of pleasure from regrowth would stack if she lost multiple torsos at once, so she summoned two more scythes and tried cutting three of her hydra necks all at once. Unable to hold back, she practically shrieked in bliss at the tripled feeling of growing new bodies, and it took all her willpower not to cum right then and there. Now sporting nine necks and torsos, Fionna made a mental note that she would have to be careful not to get addicted to the euphoria of splitting further. Finally, to test her hypothesis about how many clones of herself she could make, Fionna reasoned that she should be able to have up to twelve bodies now, since she had absorbed eight new girls. Turning her body translucent and gelatinous again, Fionna willed herself to split in two, then repeated this again and again. As expected, she reached her limit at a dozen bodies, and reveled in the possibilities this afforded her now.
Turning to the mansion...