PUZZLES #17-20: "Highway to the Stranger Zone"/"Play Again?"/"Roamin' Empire"/"Steep Descent"

[pascop...@gmail.com]

Here's four puzzles all at once, because I'm bad at remembering to update the Google Group. Hopefully you've been keeping up on the puzzles by going to the site. If not, I'm expressly sorry, and I hope you consider this update to be a reconciliatory gift of four new puzzles. 

The "Stranger Zone" puzzle is a meta, with instructions found here.

Happy solving!

-Paolo