Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature you control may become lethal if The Walls of Ba Sing Se leave the battlefield during that turn
I built around them both with stuff like Hei Bei, Joo Dee and Buzzard-Wasp Colony too, and then the one mentioned above too
If you want something more exploitive of Behold the Beyond, how about Seasons Past
Find the right way to create graveyard value, and youll buy yourself a victory
Kamigawa: Neon Dynasty Set Booster Pack $12.99 US Shipping Only Due to export restrictions, this item may only be shipped to addresses in the United States, APO/FPO addresses, and Puerto Rico
This is a great, reliable form of ramp for green decks that can be played early for a quick head start