Cast Time Walk by paying ({1} magic symbol) ({U} magic symbol) , causing you to take an extra turn after this one.
Cast Mystic Retrieval by paying ({3} magic symbol) ({U} magic symbol) , returning Runic Repetition to your hand from your graveyard.
Cast Mystic Retrieval from your graveyard for its flashback cost by paying ({2} magic symbol) ({R} magic symbol) , returning Time Walk from your graveyard to your hand and exiling Mystic Retrieval.
Cast Runic Repetition by paying ({2} magic symbol) ({U} magic symbol) , returning Mystic Retrieval from exile to your hand.
Repeat each turn.
Results
Infinite turns.
Instant/Sorcery with "Return Instant/Sorcery from GY to hand".