Actor Mark Ruffalo attends 'Avengers: Age of Ultron' premiere at Indigo Mall on April 19, 2015 in Beijing, China.

"Avengers: Age of Ultron" this weekend, tracking for a $187.7 million opening and having already hauled in $255 million in its first week overseas.

Yet even after the final figures for the domestic debut roll in, Earth's Mightiest Heroes have another challenge: conquering the Chinese box office.