Cast Invasion of Arcavios by paying ({3} magic symbol) ({U} magic symbol) ({U} magic symbol) .
When Invasion of Arcavios enters the battlefield, it triggers, returning Beacon of Tomorrows from your graveyard to your hand, or searching your library for Beacon of Tomorrows and putting it into your hand, if needed.
Cast Beacon of Tomorrows by paying ({6} magic symbol) ({U} magic symbol) ({U} magic symbol) .
Brinelin triggers, returning Invasion of Arcavios to your hand from the battlefield.
Resolve Beacon of Tomorrows, causing you to take an extra turn after this one and shuffle it into your library.