So, you know how in some stories there are characters called vampires? They're like really pale people with sharp teeth who drink blood to stay alive. Well, in some places, people used to believe that vampires were real and could be dangerous.
That's where the krsnik comes in! A krsnik is like a special kind of superhero who is really good at hunting down vampires. They are usually men, and they wear special clothes with symbols and patterns on them to protect themselves from the vampires.
Krsniks also have special powers like being able to turn invisible or summoning powerful creatures to help them in their fights. They also know a lot about herbs and potions that can hurt or even kill vampires.
So, if there ever were vampires in their village or town, people would call on the krsnik to come and take care of them. And everyone would feel safer knowing that someone like the krsnik was there to protect them.