Scaretiller and Retreat to Coralhelm on the battlefield.
Scaretiller is untapped.
You have a basic Forest, Plains or Mountain in library.
Steps
Play Cabaretti Courtyard.
Cabaretti Courtyard enters the battlefield, triggering itself and Retreat to Coralhelm.
Resolve the Cabaretti Courtyard trigger, causing you to sacrifice it, then search your library for a basic Forest, Plains or Mountain 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 Cabaretti Courtyard from your graveyard to the battlefield tapped.
Cabaretti Courtyard enters the battlefield, triggering itself and Retreat to Coralhelm.
Resolve the Retreat to Coralhelm trigger, untapping Scaretiller.
Repeat from step 3.
Results
Near-infinite landfall triggers.
Near-infinite lifegain.
Near-infinite lifegain triggers.
Put all basic Forests, Mountains, and Plains from your library onto the battlefield tapped.