Ask the students to tell you a folk tale/myth from their country. If no one wants to you tell them one from yours.
Ask the students to try to finish the first part of the lessons "Bad Monsters" by themselves. Then go through each one of them and discuss it with them - abilities/story/how to kill etc. This should take at least an hour.
Go to Part 2 called "Good Mythical Creatures" Do the same as in Exercise 1. Keep the discussion going.