Play a land. When the land enters, Springheart Nantuko triggers, causing you to pay 1 to create a token copy of Dryad Arbor.
When the Dryad Arbor token enters, Springheart Nantuko triggers. Holding priority, activate the Dryad Arbor token by tapping it, adding .
Nissa, Who Shakes the World triggers, adding .
Resolve the Springheart Nantuko trigger, causing you to pay 1 to create a token copy of Dryad Arbor.
Repeat from step 2.
Activate Nissa's first loyalty ability by putting a loyalty counter on it, animating a Forest you control.
Cast Springheart Nantuko for its bestow cost by paying 1, attaching it to the animated Forest.
Activate the animated Forest by tapping it, adding .
Nissa triggers, adding .
Play a land.
When the land enters the battlefield, Springheart Nantuko triggers, causing you to pay 1 to create a token copy of the Forest it is attached to.
When the Forest token enter the battlefield, Springheart Nantuko triggers.
Holding priority, activate the Forest token by tapping it, adding .
Nissa triggers, adding .
Resolve the Springheart Nantuko trigger, causing you to pay 1 to create a token copy of the Forest it is attached to.
Repeat from step 6.
This clever loop uses Springheart Nantuko to continuously copy a land-creature while a mana-doubling engine covers the activation costs. By bestowing Springheart Nantuko onto a land animated by Nissa, Who Shakes the World, every landfall trigger generates a token copy of that land-creature, which can be immediately tapped alongside Nissa's static ability to easily pay for the next landfall payload. Meanwhile, Dryad Arbor provides the initial creature foundation for the loop, and Urabrask the Hidden ensures that your massive tide of token arrivals ignores summoning sickness entirely.