Consider the plant monster from Hellboy II or the eyeless creep in Pan's Labyrinth: Director Guillermo del Toro has a genius for putting bizarre beings on screen. But no matter how grotesque the vision, he always begins his creations with what he calls "the National Geographic approach." Start with a nightmarish idea, and then look to nature for details. "You want to make the creatures outlandish enough that they'll thrill the imagination," he says, "but recognizable enough that they feel…