How do you get the Demoncursed Vayne Border Icon?
It came in a bundle. Riot's description in the client reads: “An icon that entitles the border for this champion.”
Is the Demoncursed Vayne Border Icon still available?
Maybe, while it lasts. Riot tied the Demoncursed Vayne Border Icon to 2026 (bundle). It does not normally bring back event rewards or bundles once they end.
