How do you get the Darkin Rhaast Icon?
It was a mission or event reward. Riot's description in the client reads: “Earned by completing missions during the release of Kayn.”
Is the Darkin Rhaast Icon still available?
No. Riot tied the Darkin Rhaast Icon to 2017 (mission reward), and it does not normally bring back past event rewards or bundles.
