Springheart Nantuko + Roaring Earth + Primal Vigor

Prerequisites

You control a Forest that enters the battlefield untapped.

Steps

1. Animate a Forest that enters untapped using Roaring Earth
2. Cast Springheart Nantuko for its bestow cost by paying {1}{G}, attaching it to the animated Forest.
3. Play a land. When the land enters, Springheart Nantuko triggers, causing you to pay {1}{G} to create two token copies of the Forest that enters untapped.
4. When the Forest tokens enter, Springheart Nantuko triggers twice.
5. Holding priority, activate the Forest tokens by tapping them, adding {G}{G}.
6. Resolve the first Springheart Nantuko trigger, choosing not to pay and creating two 1/1 Insect creature tokens.
7. Resolve the second Springheart Nantuko trigger, causing you to pay {1}{G} to create two token copies of the Forest that enters untapped.
8. Repeat from step 4.