Activate all mana-producing lands you control by tapping them, adding at least {4}{R}{G}{W}.
Cast Zacama either from your hand or from the command zone by paying {6}{R}{G}{W} plus commander tax, if applicable.
When Zacama enters the battlefield, it triggers twice.
Resolve the first trigger, untapping all lands you control.
Activate all mana-producing lands you control by tapping them, adding at least {4}{R}{G}{W}.
Resolve the second Zacama trigger, untapping all lands you control.
Cast Shivan Wurm by paying {3}{R}{G}.
When Shivan Wurm enters the battlefield, it triggers twice, returning itself and Zacama from the battlefield to your hand.
Repeat.
If lands you control can tap to produce at least {5}{R}{G}{W}, this combo nets infinite mana, and you may use that mana to activate Zacama's other abilities.

Destroy all artifacts and enchantments opponents control

Infinite damage to creatures

Infinite creature ETB

Infinite lifegain

Infinite lifegain triggers

Infinite creature LTB

Infinite mana lands you control can produce

Infinite storm count

Zacama, Primal Calamity

Panharmonicon

Shivan Wurm

Elesh Norn, Mother of Machines

Cast Shivan Wurm by paying {R}{G}.
Birgi, Animar and Tangleroot trigger.
Resolve the Tangleroot and Birgi triggers, adding {R}{G}.
Resolve the Animar trigger, putting a +1/+1 counter on it.
When Shivan Wurm enters the battlefield, it triggers, returning itself from the battlefield to your hand.
Repeat.

Infinite +1/+1 counters on a creature

Animar, Soul of Elements

Birgi, God of Storytelling // Harnfel, Horn of Bounty

Tangleroot

Combos with "Shivan Wurm"