I don't really like to "foreshadow" all that much. As a writer, I've kind of felt that was me not being able to "reign in" my over-excited desire to tell the audience what as going on. I've also always felt like it was me thinking I was smarter than my audience and that they'd totally not figure things out with my foreshadowing (pro tip, your audience is often smarter than even you are).
I like to have "unknowns" instead. That is, things work the way they work for a concrete planned out reason... And the audience is never clued into what that reason is. The audience can speculate or guess, and that's good enough for me. There's a definite answer for things being the way they are and it makes a perfect logical sense. But, the characters don't know and neither does the audience.
I find it's much easier to restrain myself that way. If an audience member figures it out, then that's great for them. If they don't, then they get to maybe enjoy the mystery.
Why were my Elves beast people and then how did they change into the familiar fantasy style Elves? Why did that happen? Are the stories they tell real or are they steeped in analogy? Why do they guard a dead city?
The audience will probably never know. But, I know.