This is really more a danger than a monster, something like green slime.
Devil’s rope is a vine that grows from the top of cliffs and hangs about 10 to 20 feet. The vine is a greenish-brown and looks corded like a rope. At the bottom there hangs a deep purple gourd filled with bitter flesh and seeds that can be crushed to form a primitive flash powder.
After the first five feet, the vine becomes increasingly sticky, requiring those who are in contact with the lower portion to pass a Strength test (Fortitude save modified by Strength or save vs. paralysis) to unstick themselves. Naturally, if they keep climbing down, they must make this save every couple feet. Once somebody is stuck (i.e. fails a save), they are stuck for good unless somebody else removes them using a dagger (1d4 damage to the hands), boiling water (1d6 fire damage) or magic of some kind. A grease spell might work, though one would slip off the vine and fall. Most victims are simply stuck fast and die on the vine, their rotting flesh and clothing eventually allowing their corpses to fall from the vines and litter the ground below.