Infinite combat damageInfinite combat phasesInfinite magecraft triggersInfinite storm countInfinite mana lands you control can produceInfinite untap of lands you control
How it works
Declare Hellkite Charger and the creature with Spellbinder attached as attackers, triggering Hellkite Charger.
Holding priority, activate all mana-producing lands you control by tapping them, adding at least 5.
Resolve the Hellkite Charger trigger, causing you to pay 5 to untap all attacking creatures and get an additional combat phase after this one.
Deal combat damage with the creature that has Spellbinder attached.
Spellbinder triggers, casting a copy of Turnabout without paying its mana cost.
Resolve Turnabout, untapping all tapped lands you control.