Dream Halls and Conspiracy Theorist on the battlefield.
Steps
Cast Petals of Insight by discarding Aethertide Whale.
Conspiracy Theorist triggers, exiling Aethertide Whale and allowing you to cast it from exile this turn.
Resolve Petals of Insight, putting the top three cards of your library on the bottom of your library, and returning Petals of Insight to your hand.
Cast Aethertide Whale from exile by discarding Petals of Insight.
Conspiracy Theorist triggers, exiling Petals of Insight and allowing you to cast it from exile this turn.
Aethertide Whale enters the battlefield, causing you to get six ({E} magic symbol) .
Activate Aethertide Whale by paying ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) , returning it to your hand from the battlefield.
Cast Petals of Insight from exile by discarding Aethertide Whale.