Will the gameplay be more story based, or will you have to complete objectives while events happen?
The second idea could work really well in my opinion, for an example you can't be near water when bubbles start to rise, you have to get inside when some sound or visual cue starts. My idea would have multiple monsters and you kind of have a time limit, it's going to get dark and the events will happen more frequently. So you have to complete your objectives as fast as you can, take risks, but at the same time be careful. (Drop your buckets and oluet and run to a safe spot!)
That kind of gameplay could be really interesting, terrifying at first, when you don't know about the events, and keep the tensions rising. You could also make different modes with the existing events and stuff.
Just an idea, thought it would be a cool way to use the setting and Finnish folklore. Whatever route you go down, I hope you make the game you wanted!