Play Riveteers Overlook.
When Riveteers Overlook enters, it and Retreat to Emeria trigger.
Resolve the Retreat to Emeria trigger, creating a 1/1 Kor Ally creature token.
When the Kor Ally enters, Haru triggers, earthbending Riveteers Overlook.
Resolve the Riveteers Overlook trigger from step 2, causing you to sacrifice it, search your library for an applicable land and put it onto the battlefield tapped, and gain 1 life.
Haru triggers, returning Riveteers Overlook from your graveyard to the battlefield.
Repeat from step 2.

Infinite ETB

Infinite lifegain triggers

Infinite lifegain

Infinite creature tokens

Near-infinite landfall triggers

Infinite landfall triggers

Put all basic Mountains from your library onto the battlefield tapped

Put all basic Forests from your library onto the battlefield tapped

Put all basic Swamps from your library onto the battlefield tapped

Retreat to Emeria

Haru, Hidden Talent

Riveteers Overlook

Play Riveteers Overlook.
Riveteers Overlook enters the battlefield, triggering itself and Retreat to Coralhelm.
Resolve the Riveteers Overlook trigger, causing you to sacrifice it, then search your library for a basic Mountain, Swamp or Forest card, put it onto the battlefield tapped, and gain 1 life.
The basic land enters the battlefield, triggering Retreat to Coralhelm, tapping Scaretiller.
Scaretiller triggers, returning Riveteers Overlook from your graveyard to the battlefield tapped.
Riveteers Overlook enters the battlefield, triggering itself and Retreat to Coralhelm.
Resolve the Retreat to Coralhelm trigger, untapping Scaretiller.
Repeat from step 3.

Near-infinite lifegain

Near-infinite lifegain triggers

Put all basic Swamps, Forests, and Mountains from your library onto the battlefield tapped

Scaretiller

Retreat to Coralhelm

Activate Clock of Omens by tapping Scaretiller and another artifact, targeting Scaretiller.
Scaretiller triggers, returning Riveteers Overlook from your graveyard to the battlefield.
Riveteers Overlook enters the battlefield, triggering itself and Toggo.
Resolve the Toggo trigger, creating a Rock equipment token.
Resolve the Riveteers Overlook trigger, causing you to sacrifice it then search your library for a basic Forest, Mountain, or Swamp and put it onto the battlefield.
If you put a land onto the battlefield this way, Toggo triggers, creating a Rock equipment token.
Resolve the Clock of Omens ability from step 1, untapping Scaretiller.
Repeat.

Infinite tapped Rock tokens

Toggo, Goblin Weaponsmith

Clock of Omens

Play Riveteers Overlook.
Riveteers Overlook enters the battlefield, triggering itself and Stone-Seeder Hierophant.
Resolve the Stone-Seeder Hierophant trigger, untapping it.
Activate Stone-Seeder Hierophant by tapping it, untapping any land you control.
Resolve the Riveteers Overlook trigger, causing you to sacrifice it, then search your library for a basic Forest, Swamp or Mountain card, put it onto the battlefield tapped, and gain 1 life.
The basic land enters the battlefield, triggering Stone-Seeder Hierophant, untapping Stone-Seeder Hierophant.
Activate Stone-Seeder Hierophant by tapping it, untapping Scaretiller.
Activate Scaretiller by tapping it, adding {G}.
Scaretiller triggers, returning Riveteers Overlook from your graveyard to the battlefield tapped.
Repeat from step 2.

Near-infinite mana lands you control can produce

Put all basic Forests, Mountains, and Swamps from your library onto the battlefield tapped

Ashaya, Soul of the Wild

Stone-Seeder Hierophant

Activate Scaretiller by tapping it, adding {1}.
Scaretiller triggers, returning Riveteers Overlook from your graveyard to the battlefield tapped.
Riveteers Overlook enters the battlefield, causing you to sacrifice it and search your library for a basic Mountain, Swamp or Forest and put it onto the battlefield tapped.
Activate Voltaic Construct by paying {2}, targeting Scaretiller.
Illusionist's Bracers triggers, copying Voltaic Construct's ability, targeting Scaretiller.
Resolve the copy of Voltaic Construct's ability, untapping Scaretiller.
Holding priority, repeat steps 1 through 3 one additional time.
Resolve the original Voltaic Construct's ability, untapping Scaretiller.
Repeat.

Put all basic Swamps, Forests, and Mountains from your library onto the battlefield

Voltaic Construct

Paradise Mantle

Illusionist's Bracers

Activate Scaretiller by tapping it, targeting Cacophodon.
Scaretiller triggers, returning Riveteers Overlook from your graveyard to the battlefield tapped.
Riveteers Overlook enters the battlefield, triggering itself and Roaring Earth.
Resolve the Roaring Earth trigger, putting a +1/+1 counter on Cacophodon.
Resolve the Riveteers Overlook trigger, causing you to sacrifice it and search your library for a basic Mountain, Swamp or Forest and put it onto the battlefield tapped.
If you put a land onto the battlefield this way, Roaring Earth triggers, putting a +1/+1 counter on a creature you control.
Resolve the Scaretiller ability from step 1, dealing 1 damage to Cacophodon.
Cacophodon triggers, untapping Scaretiller.
Repeat.

Infinite +1/+1 counters on Cacophodon

Cacophodon

Viridian Longbow

Roaring Earth

Combos with "Riveteers Overlook"