I was a child in Germany but don't remember what program I may have watched this on. I also don't remember if the original language was German or if it was dubbed over hence why I put in the title "European".
What I remember is that it seems like a young adult friend group (as a child I thought they were adults, so think late teens early 20s) goes to the countryside for a vacation I believe. One of the couples of the friend group is talking along the road when suddenly someone on a horse grabs the girl and magically zips through a portal. I don't remember how the rest of the people get to this fantasy land but they do. It is an old timey/medieval world and this friend group has to traverse through the countryside to try and get their friend back. However, there is some sort of evil magic trying to separate them/make them all turn against each other and when they give into this evil, they seemingly die but its not clear - they vanish into smoke. That is a big part I remember. Someone grabs onto a faulty rock/ladder/ledge and falls and poofs into smoke , she is one of the first to go. Towards the end, when its a girl and two guys, she sees this scarecrow? with a beautiful necklace and goes to take it and poofs away. The big climax is the two guys saying they will work together but then the big evil turns the non-main character guy against our hero. I think in the end everyone is returned? I don't really remember.