If you’ve been following director-writer Guillermo del Toro, you know him as the horror master behind "The Shape of Water," "Pan’s Labyrinth," "Nightmare Alley" and the recent "Frankenstein," which is earning accolades this awards season. His work is defined by richly imagined worlds, tragic monstersand a fascination with creatures lurking just beneath the surface of everyday life. That imaginative streak has also spilled into comic-book TV adaptations like "Hellboy," but del Toro’s most unsettling creatures tend to appear when he’s free to fully reshape mythology on his own terms. Few projects demonstrate that better than "The Strain," a series that...