When Arid Archway enters the battlefield, it, Thranduil, Sindarin Liege, and Kodama of the East Tree trigger.
Resolve the Kodama of the East Tree trigger, choosing not to put anything from your hand onto the battlefield.
Resolve the Arid Archway trigger, returning it from the battlefield to your hand.
Resolve the Thranduil, Sindarin Liege trigger, creating a token.
When the token enters the battlefield, Kodama of the East Tree triggers, putting Arid Archway from your hand onto the battlefield.
When Arid Archway enters the battlefield, it and Thranduil, Sindarin Liege trigger.
Repeat from step 4.
This clever loop turns the self-bouncing nature of Arid Archway into a continuous engine by leaning on Kodama of the East Tree to instantly cheat the land back into play whenever a permanent enters. Meanwhile, Thranduil, Sindarin Liege provides the vital bridge via its landfall ability, generating a fresh Elf token each time the land drops to satisfy Kodama of the East Tree's trigger condition. Together, this trio creates an endless cycle of entering and returning that floods your board with an unstoppable wave of creature tokens and triggers.