"hmmm..." aunt Carol pondered as she looked over the vial "actually if I recall being told correctly when having the vials' effects explained to me, taking a little either just courses a small change in a random area for a limited time based on the amount...though their were suggestions it was instead a second transformed per drop, only getting infinite time from a whole vial".
"so which-" Mary started as aunt Carol got back up and handed the vial back to Mary. "your choice of transformation, your right to try the form first" aunt Carol stated kindly. "...you sure?" Mary questioned. "absolutely" aunt Carol assured.
taking a precaution Mary sat down onto the sand with her legs laying flat to avoid a painful fall "alright... bottoms up" Mary said aloud as she downed the vial's liquid and again handed the vial to aunt Carol.
suddenly Mary felt it as her body went through the process, her legs moved tightly together and were locked by her skin merging them into a single limb, her toes extended and branched out to form an exoskeleton of sorts.
"huh... not much-" aunt Carol started before both she and Mary witnessed purple scales (Mary's favourite colour) start form all over her body from the waist below while a lighter purple membrane formed apart of the exoskeleton to create Mary's tailfin.
"you were saying aunt Carol?" Mary questioned before more changes happened, webbing matching the tailfin formed between Mary's fingers while the skin from her hands to her elbows was covered in the purple scales. then branches grew out from her scaled forearms with webbing accompanying them and as this happened a similar process occurred on Mary's back but in a slightly larger scale.
"OK... now that's forms more speed based then attractive-" aunt Carol started to remark. but was interrupted by the sight for Mary's ears becoming fined-like and her breasts expanding from B-cup to D-cup size with scales now covering them and finally, slit like openings appeared on Mary's neck.
"MARY ARE YOU OK?" Aunt Carol shouted once it was clear the process was truly finished. "ummm... hello, of course and i'm fine" Mary answered in distaste in want was to her aunt Carol's overdone reaction. "but your neck... those openings-" aunt Carol tried to point out. "must be gill slits... many fish have them so logically mermaids have both them and lungs for breathing" Mary pointed out, relieving aunt Carol.
"now while you get changed, i'm going to go swimming" Mary then announced. "swimming? what about them rocks? what about singing? attracting sailors like moths-" aunt Carol argued. "what about the wonders of the deepest blues? of the millions of sunken ships filled with treasure?" Mary interrupted before dragging herself off towards the water.
"oh Mary... still such a tomboy, I was so adamant that you choosing mermaids could have meant you were starting to discard that adventurous spirit of your" Aunt Carol sadly ranted as she returned to the cabinet to refill the vial: