All permanents on the battlefield (Springheart Nantuko attached to Dryad Arbor).
You have at least one land card in hand.
You are able to play a land this turn.
You control at least one basic Forest, or the land card in your hand is a basic Forest.
({1} magic symbol) ({G} magic symbol) available.
Steps
Play any land from your hand, ensuring to play a basic Forest if you have one in hand.
When the land enters the battlefield, Springheart Nantuko triggers, causing you to pay ({1} magic symbol) ({G} magic symbol) to create three token copies of Dryad Arbor.
When the Dryad Arbor tokens enter the battlefield, Springheart Nantuko triggers three times.
Holding priority, activate a basic Forest by tapping it, adding ({G} magic symbol) .
Activate Earthcraft by tapping a Dryad Arbor token, untapping the basic Forest.
Repeat steps 4 and 5 one additional time.
Resolve the first and second Springheart Nantuko triggers, choosing not to pay and creating six 1/1 Insect creature tokens.
Resolve the second Springheart Nantuko trigger, causing you to pay ({1} magic symbol) ({G} magic symbol) to create three token copies of Dryad Arbor.
Repeat from step 3.
Results
Infinite creature tokens.
Infinite ETB.
Infinite Forest tokens.
Infinite landfall triggers.
Infinite mana basic lands you control can produce.