My PCs recently derailed a whole bunch of my planning through creative play – which is fine, the surprises make the game more entertaining for me this way – they ended up in the Slumbering Ursine Dunes and here are converted monsters for my own reference with abbreviated 5e stat blocks.
A particularly nasty example of the inimical Pahr spirit is the vodník, a male water nymph
of a, particularly sour and murderous nature. Vodník often lurk at the edges of lakes and
rivers waiting for lone wanderers or small groups of village folk.
Water Bound. The vodnik dies if the water to which he is bound is destroyed. Casting purify food and water on the creature kills it outright.
Drown. Melee Weapon Attack: +5 to hit, reach 10 ft., one creature. Hit: 3d6 bludgeoning damage. If the target is Medium or smaller, it is grappled (escape DC 13) and pulled 5 feet toward the vodnik. Until this grapple ends, the target is restrained, the vodnik tries to drown it, and the vodnik can’t drown another target.
Shapechanger. The vodnik can use its action to polymorph into a Large watery snake, or back into its true form, which is a scaly potbellied male humanoid. His statistics are the same in each form. Any equipment he is wearing or carrying is also transformed. It reverts to its true form if it dies.