Rex, Cyber-Hound, Trench Behemoth, and Skyshroud Ranger

Prerequisites

• Rex, Cyber-Hound on the battlefield
• Trench Behemoth in exile
• Skyshroud Ranger in exile
• You have at least one land card in hand
• Rex does not have summoning sickness
• Trench Behemoth and Skyshroud Ranger exiled with brain counters on them

Steps

1. Activate Rex using Skyshroud Ranger's ability by tapping it, putting a land from your hand onto the battlefield
2. If the land is mana-producing and enters the battlefield untapped, you may activate it by tapping it, adding at least
3. Activate Rex using Trench Behemoth's ability by returning the land from the battlefield to your hand, untapping Rex
4. Repeat

Results

• Infinite landfall triggers
• Infinite mana lands you control that enter the battlefield untapped can produce