The water leaper is a fairly straightforward and basic monstrosity, the kind that I might even allow as a beast in supernatural worlds. They’re essentially a snake/frog/scorpion/bat. A snake with a frog’s head, a bat’s wings, and a poisonous stinger at the end of its tail. They’re very slow and weak on land, but are fast fliers and swimmers, so their hunting is mostly limited to rivers, lakes, and those swamps with enough deep water to maintain regular hunting territory for one.
Alternatively to it being an actual natural creature, they may be the creation of a wizard looking to get their name out there for designing biological weapons. The next owlbear, as they say.
A thieves’ guild has a pair of water leapers brought north to guard the underwater tunnel to their smuggling den. The creatures manage to escape however, and outside their normal territory find they have few natural predators to deal with them. Their flight lets them jump from lake to lake, outpacing the regular threats of the region and the defenses people have developed to deal with them. The thieves want the leapers recaptured, while local druids worry if the potentially mating pair have left any egg clumps behind in their cross country journey.
Water leapers usually restrain their hunting to deer and the occasional crocodile, but one has become a maneater. Sick from devouring an undead deer, it was driven from its usual hunting grounds by healthy rivals. In desperation it attacked and killed a human farmer, and found that they were generally easy prey. It began associating the various humanoids of the region as prey, and aggressively stalks boaters and isolated travelers who are used to water leapers leaving them alone. Unfortunately it will have to be put down, but its high mobility and cunning will make it a difficult target and skilled trackers will be needed.
Why do so many wizards get caught up in creating some new monster? There are very few cases of them being easily controllable for military purposes, and no one can come up with any other practical reason for creating something like the owlbear. Except for pride, and to prove that they are capable of something only the gods are supposed to be, the creation of new life. At least, that’s what drove the creator of the water leaper, a smug, atheistic wizard who sought to show up the nearby temples. In response to the argument that only the divine can create, he magically fused together a number of different creatures and unleashed the resulting monster on the temple. Now half a dozen acolytes are dead, and the creature has flown toward town, driven by the conflict of so many different hunting instincts.
Writing and Rolling 