Cast Turnabot by paying ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) , untapping at least eight lands.
Cast a copy of
Regrowth from exile by paying ({1} magic symbol) ({G} magic symbol) , targeting [[Untapper]].
Spellweaver Helix's last ability triggers, allowing you to cast the Extra Combat Sorcery, giving you an additional combat phase and an additional main phase this turn.
Resolve the copy of
Regrowth, returning
Turnabout from your graveyard to your hand.
Declare
Emeritus of Abundance as an attacker.
When
Emeritus of Abundance attacks, it triggers, becoming prepared.
Repeat each main phase.
Notes
Note that this does not work with cards that care about the "first postcombat main phase" or similar, such as World at War.