How do you get the 00 Reactivated Icon?
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 2016.”
Is the 00 Reactivated Icon still available?
Probably not. Riot tied the 00 Reactivated Icon to 2016 (store purchase), and it does not normally bring back past event rewards or bundles.
