Levitation, with the assumption that the potion requires enough build up to take effect, and that's unpredictable. People spontaneously start floating, without precise control over their altitude. Over time, they acclimate, gain control, and a whole system of rooftop gardens and storage/industry has emerged, leading to nets and ropes being strung everywhere for horizontal movement. Long term exposure is causing the weight of everyone in the village to decrease, and some children have been born that seemingly can't touch the ground, repelling a limited distance above it at all times.