When Coral Atoll 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 Coral Atoll.
Resolve the Coral Atoll trigger from step 2, causing you to sacrifice it
Haru triggers, returning Coral Atoll from your graveyard to the battlefield.
Repeat from step 2.
This clever loop hinges on Coral Atoll’s self-sacrificing entry condition to continuously cycle the land back and forth, turning a simple bounce into a relentless engine. Each time Coral Atoll hits the battlefield, Retreat to Emeria rewards your landfall with a fresh Kor Ally token, which in turn triggers Haru, Hidden Talent to earthbend that very same land into a creature. When Coral Atoll is inevitably forced to sacrifice itself to its own trigger, Haru's delayed effect immediately rescues it from the graveyard, setting up the loop to start all over again.