Lumra, Bellow of the Woods + Mirrorpool + Coastal Hornclaw + Horizon Explorer

Lumra, Bellow of the Woods

Mirrorpool

Coastal Hornclaw

Horizon Explorer

How it works

1. Activate any number of other lands by tapping them, adding at least 4C.
2. Activate Coastal Hornclaw by sacrificing a land except Mirrorpool.
3. Repeat step 2 until you control no lands except Mirrorpool.
4. Activate Mirrorpool's third ability by paying 4C, tapping and sacrificing it, creating a token copy of Lumra.
5. Put the Lumra token into your graveyard due to the legend rule.
6. The Lumra token's enters-the-battlefield ability triggers, causing you to mill four cards and return all land cards from your graveyard to the battlefield untapped due to Horizon Explorer.
7. Repeat.

This intricate loop scales your mana base while continuously recycling your graveyard to trigger massive creature deployment. You begin by using Coastal Hornclaw to clear away your lands—while Horizon Explorer ensures your lands will later reenter untapped—leaving Mirrorpool as the sole remaining land so it can be sacrificed to copy Lumra, Bellow of the Woods. The legend rule promptly sends the token copy to the graveyard, which triggers Lumra's ability to mill four cards and flood the battlefield with every land card in your graveyard. Because Horizon Explorer is on the field, all those returning lands immediately enter untapped to pay for the next iteration, letting you repeat the process indefinitely.