Call to Mind in your graveyard, with the other in your hand
Chandra on the battlefield
Walk the Aeons in hand
You have not cast an instant or sorcery this turn
({4} magic symbol) ({U} magic symbol) ({U} magic symbol) available on each odd-numbered turn, with at most ({3} magic symbol) ({U} magic symbol) available each even-numbered turn
Steps
Cast
Walk the Aeons by paying ({4} magic symbol) ({U} magic symbol) ({U} magic symbol)
Chandra triggers, copying
Walk the Aeons
Resolve both
Walk the Aeonss, causing you to take two extra turns after this one
Move to your next turn
Cast etiher
Mystic Retrieval or
Call to Mind by paying its mana cost, targeting either