For more detailed instructions, look to hyogi's original post: https://www.altopedia.net/activities/1924-detective-pikachu-on-the-case
I changed the game so that there are 5 mysteries and the students practice helping verbs. I also don't have access to Canva, so I changed some of the pictures in the presentation. I am at an inaka lower level high school and did this lesson with my first years. For my lower level classes, we got through 4 mysteries in 45 minutes. For my highest level class, we got through the fifth one as well.
Because my students don't ever volunteer for things, I put them in groups of 5 after the discussion question warm up. I would call on one group to be the suspects and another group to be the detectives. For the fourth mystery, I explain to the students before starting that we don't usually write "can't've", but we often say helping verbs this way. That way they can practice speaking more casually. At the end, I also added some slides so that I could explain the difference between May/Can, Must, Musn't, and Should/Had better. This isn't necessary for the game, I just do it to fill time when the class finishes a little bit early.
I've uploaded everything in Powerpoint so that they can be edited.