Location: Gascony
Cryptids, Undead
by @drferno
A hopping leg with an eye on the knee, said to run down mountains at night to scare people; some kind of boogeyman.
Two Gascon tales collected by Jean-François Bladé refer to a leg stolen from a dead person. It is not just a sentient leg on its own, but this could be considered a possible origin.
However, it is more likely that we have to go back much further: the Celtic god Lugh is depicted leaping on one leg, one eye closed, waving one arm, before the battle of Magh Tuireadh (or Samhain). There are numerous representations of figures sitting on one leg.