How do you get the Carnival 2014 - Carnival Mask?
It was a mission or event reward. Riot's description in the client reads: “Earned by playing one game during the Carnival event in Brazil and Latin America or purchased in other regions in 2014.”
Is the Carnival 2014 - Carnival Mask still available?
No. Riot lists the Carnival 2014 - Carnival Mask as a legacy icon. Legacy icons are out of regular rotation and return only during occasional events or promotions.
