Skyshroud Ranger does not have summoning sickness.
You have a land card in hand.
You control at least seven lands.
Steps
Activate Skyshroud Ranger 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 Skyshroud Ranger.
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.