Mirrorpool + Splendid Reclamation + Spelunking + Trenching Steed

Mirrorpool

Splendid Reclamation

Spelunking

Trenching Steed

How it works

1. Cast Splendid Reclamation by paying 3.
2. Holding priority, activate any number of lands you control except Mirrorpool by tapping them, adding at least 2C.
3. Activate Trenching Steed by sacrificing a land other than Mirrorpool.
4. Repeat step 3 until Mirrorpool is the only land you control.
5. Activate Mirrorpool's second ability by paying 2C, tapping and sacrificing it, copying Splendid Reclamation.
6. Resolve the Splendid Reclamation copy, returning all land cards from your graveyard to the battlefield untapped due to Spelunking.
7. Repeat from step 2.

By using Trenching Steed to systematically sacrifice your lands one by one, you clear the board until Mirrorpool stands alone as your sole remaining land, perfectly poised to copy a spell. When you cast Splendid Reclamation, you tap your lands for mana and feed them to the Steed to fuel Mirrorpool's second ability, allowing you to copy the massive sorcery while sacrificing the land itself. The crucial static ability of Spelunking ensures that when the copied Splendid Reclamation resolves, every single land returned from your graveyard enters the battlefield untapped instead of tapped. This provides a fresh supply of lands and mana to repeat the entire loop indefinitely, generating infinite landfall triggers, card draw, and mana.