Romana II + Mutable Explorer + Retreat to Coralhelm + Horizon Explorer

Romana II

Mutable Explorer

Retreat to Coralhelm

Horizon Explorer

How it works

1. Cast Mutable Explorer by paying 2.
2. When Mutable Explorer enters the battlefield, it triggers, creating an untapped Mutavault land token due to Horizon Explorer.
3. When the Mutavault token enters the battlefield, Retreat to Coralhelm triggers, untapping Romana II.
4. Activate the Mutavault token by tapping it, adding C.
5. Activate Romana II by paying 1 and tapping it, creating a tapped copy of the Mutavault token.
6. Repeat from step 3.

This engine leverages Horizon Explorer to ensure that any land token entering the battlefield does so completely untapped, instantly tripping the landfall ability of Retreat to Coralhelm to untap Romana II. With Romana II able to copy the freshly spawned Mutavault token (which brings changeling utility via Mutable Explorer's token-generating legacy), you can continuously tap that Mutavault for mana to fund the copying process over and over again. The result is a perpetual loop that floods your board with an endless sea of land tokens while fueling an infinite cascade of landfall triggers.