In Finnish folklore there's a couple of scary things but the one that pops to my mind is the water spirits. Näkki, vetehinen and hiisi. They are all slightly different but all have basically been used to scare kids to stay safe around waters or the water spirit of your choice will drown you. There's stories of them attacking boats too and trying to trick adults into drowning themselves.
In Finnish folklore there's a couple of scary things but the one that pops to my mind is the water spirits. Näkki, vetehinen and hiisi. They are all slightly different but all have basically been used to scare kids to stay safe around waters or the water spirit of your choice will drown you. There's stories of them attacking boats too and trying to trick adults into drowning themselves.