Bukavac is a mythical creature in Slavic mythology. Belief in it existed in Srijem (county near Vukovar, Croatia) and also some parts of Serbia (Belgrade county and Vojvodina).
Bukavac was sometimes imagined as a six-legged monster with gnarled horns. It lives in lakes and pools, coming out of the water during the night to make a loud noise (hence the name:buka - noise), jump onto people and animals, and strangle them.
Drekavac-Slavic Serbo-Croatian mythical creature
In 1900's dead strangled animals were found in the Croatian part of Srijem near the river of Sava and few strangled animals and a strangled human in Serbian part of Srijem (Srem).