Rex, Cyber-Hound, Trench Behemoth, and Scaled Herbalist

Prerequisites

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

Steps

1. Activate Rex using Scaled Herbalist'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