Sakura-Tribe Scout does not have summoning sickness.
You have a land card in hand.
You control at least seven lands.
Steps
Activate
Sakura-Tribe Scout by tapping it, putting a land card from your hand onto the battlefield.
When the land enters the battlefield,
Retreat to Coralhelm and
Omnath's second ability triggers.
Resolve the
Retreat to Coralhelm trigger, untapping
Sakura-Tribe Scout.
Resolve the
Omnath trigger, putting a +1/+1 counter on an Elemental you control, and then causing you to reveal cards from the top of your library until you reveal a land card and put it into your hand due to
Abundance.
Repeat.
Results
Near-infinite landfall triggers.
Put all lands from your hand and library onto the battlefield.