Piles of untouched Happy Meals littered sidewalks outside McDonald’s restaurants in Japan over the weekend, as frenzied customers scrambled to buy limited-edition sets with Pokémon cards. The promotional tie-up between McDonald’s and Pokémon ended just hours after it launched on Saturday as customers bought bulk orders of the meals to get their hands on an exclusive set of cards for resale,

The ‘little monsters’ cards are extremely popular among both children and adult superfan collectors, with some going as high as millions of dollars in value.