Activate Trench Behemoth by returning Plaza of Harmony from the battlefield to your hand, untapping it.
Play Plaza of Harmony, triggering it and Fastbond.
Resolve the Plaza of Harmony trigger, causing you to gain 3 life.
Resolve the Fastbond trigger, dealing 1 damage to you.
Activate Plaza of Harmony by tapping it, adding either {C} or one mana of any type a Gate you control could produce.
Repeat.

Infinite colorless mana

Infinite landfall triggers

Infinite lifegain

Combos with "Plaza of Harmony"