Cast Walk the Aeons by paying ({4} magic symbol) ({U} magic symbol) ({U} magic symbol) , causing you to take an extra turn after this one.
Move to your next turn.
Activate Kylox's Voltstrider's first ability by exiling Walk the Aeons from your graveyard, causing Kylox's Voltstrider to become an artifact creature until end of turn.
Declare Kylov's Voltstrider as an attacker.
Kylox's Voltstrider triggers, causing you to pay ({4} magic symbol) ({U} magic symbol) ({U} magic symbol) to cast Walk the Aeons from exile.
Resolve Walk the Aeons, causing you to take an extra turn after this one, and put Walk the Aeons on the bottom of your library.
Move to your next turn, drawing Walk the Aeons from the bottom of your library due to River Song.