Is She Your Sweet Dream

A young man buys a house at a reservoir in Croatia. A Slavic mythology creature Mare (nightmare) sees him sad at the shore and pays him a visit at night. She enters his bed and starts torturing him, but somehow they like each other and love happens. He is obsessed with his mercenary ex girlfriend and Mare suggest them to get married to revenge her. He is sure that Mare is not a bit like her. Is he doing his life mistake?