When Selesnya Sanctuary 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 Selesnya Sanctuary 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 Selesnya Sanctuary from your hand onto the battlefield.
When Selesnya Sanctuary enters the battlefield, it and Thranduil, Sindarin Liege trigger.
Repeat from step 4.
This clever loop turns the self-bouncing nature of Selesnya Sanctuary into a perpetual motion machine by pairing it with Kodama of the East Tree. Every time the land enters the battlefield, Kodama's triggered ability—waiting in reserve—uses the entry of the token generated by Thranduil, Sindarin Liege's landfall ability to immediately cheat the bounced land right back into play. Because Thranduil, Sindarin Liege also pumps your squad with a static +1/+1 buff to your Elves, you aren't just generating an endless sea of creatures and landfall triggers, but setting up a massive board state primed to overwhelm the opposition.