Activate Rex using Palladium Myr's ability by tapping it, adding {C}{C}.
Activate Rex using Pili-Pala's ability by paying {2} and untapping it, adding one mana of any color.
Repeat.

Infinite colored mana

Infinite colorless mana

Rex, Cyber-Hound

Pili-Pala

Palladium Myr

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

Combos with "Rex, Cyber-Hound"