Marvel superhero Thor hammered rivals for a second straight weekend at the North American box office, industry estimates showed Sunday. "Thor: The Dark World," the latest blockbuster based on Marvel's iconic comic book character, took a hefty $38.5 million in its second weekend, figures from Exhibitor Relations showed. Starring Australian heartthrob Chris Hemsworth as the hammer-wielding son of Odin, the movie is a follow-up to the franchise's 2011 money-spinning first instalment, "Thor." Debuting strong in second place was romantic comedy "The Best Man Holiday," a sequel 15 years in the making to "The Best Man," in which the college friends reunite over Christmas and reignite romance and rivalries.