All four options present intriguing ways that the parallel plots could intertwine to create a sense of mystery. However, the strongest option for adding a sense of mystery is:
**Events could become illogical at times in both realities to make the reader question what is really happening before the final reveal.**
This choice emphasizes the unpredictability of the story and creates a sense of confusion and intrigue, encouraging readers to engage more deeply with the narrative as they try to piece together the truth behind both realities.