Lumra, Bellow of the Woods + Mirrorpool + Thaumatog + Horizon Explorer

Lumra, Bellow of the Woods

Mirrorpool

Thaumatog

Horizon Explorer

How it works

1. Activate any number of other lands by tapping them, adding at least 4C.
2. Activate Thaumatog 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 loop relies on deliberately trimming your board down to just Mirrorpool so that copying Lumra, Bellow of the Woods results in a legendary sacrifice that instantly triggers her graveyard recursion. By feeding your other lands to Thaumatog, you clear the way for Mirrorpool's creature-copying ability while utilizing Horizon Explorer to ensure that every land card returned from the graveyard enters the battlefield untapped. Each iteration of this cycle refills your land supply, mills four cards to feed the graveyard, and triggers any landfall effects you need to overwhelm the table.