Bukavac is a mythical creature in Slavic mythology (Croatia, Serbia, Bosnia, Slovenia etc...). 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).