Walking Atlas and Bloom Tender do not have summoning sickness.
You have a land card in hand.
Steps
Activate Walking Atlas by tapping it, putting a land from your hand onto the battlefield.
The land enters the battlefield, triggering Retreat to Coralhelm twice, untapping Walking Atlas and Bloom Tender.
Activate Bloom Tender by tapping it, adding at least ({G} magic symbol) ({U} magic symbol) ({R} magic symbol) .
Activate Mina and Denn by paying ({R} magic symbol) ({G} magic symbol) and returning a land from the battlefield to your hand, giving a creature trample until end of turn.
Repeat.
Results
Infinite landfall triggers.
Infinite non-red and non-green mana among permanents you control.