God-Eternal Kefnet and Isochron Scepter on the battlefield.
({2} magic symbol) plus ({4} magic symbol) ({U} magic symbol) ({U} magic symbol) available each other turn available.
Steps
During the end step before your turn, activate Isochron Scepter by paying ({2} magic symbol) and tapping it, casting a copy of Brainstorm without paying its mana cost.
Resolve Brainstorm, causing you to draw three cards and put Walk the Aeons and another card on top of your library, ensuring Walk the Aeons is the topmost card.
Move to your turn, drawing and revealing Walk the Aeons during your draw step.
God-Eternal Kefnet's first ability triggers, causing you to pay ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) to cast a copy of Walk the Aeons.
Resolve the copy of Walk the Aeons, causing you to take an extra turn after this one.
Activate Isochron Scepter by paying ({2} magic symbol) and tapping it, casting a copy of Brainstorm without paying its mana cost.