How do you get the 2016 Worlds I MAY?
It was sold in the League of Legends store. Riot's description in the client reads: “This icon was released in the store for purchase during the 2016 Worlds event.”
Is the 2016 Worlds I MAY still available?
Probably not. Riot tied the 2016 Worlds I MAY to 2016 (store purchase), and it does not normally bring back past event rewards or bundles.
