Once Me it out and it survives to your combat step, you get to pick one of four counters to put on it
Ureni is the Dragon-specific commander here, letting you take a peek at the top eight cards of your deck when he enters or attacks and snagging a Dragon creature from among those cards and putting it directly into play

Angler's Shield Armor Wars Armorcraft Judge Become the Avalanche Biorganic Carapace Blessing of Frost Braided Quipu Chromatic Orrery Cloud, Ex-SOLDIER Collective Unconscious Coveted Falcon Distant Melody Duskana, the Rage Mother Earthshaker Dreadmaw Edgar, King of Figaro Flow of Ideas Flow of Knowledge Freyalise, Llanowar's Fury Gamma Grotesque Golden Ratio Goliath, Mass Manipulator Guild Summit Harmonized Crescendo Heirloom Epic Honden of Seeing Winds Infinite Guideline Station Inspiring Call Jackdaw Kaito, Bane of Nightmares Keruga, the Macrosage Last Stand Lunar Insight Mass Appeal Minas Tirith Garrison Mondo Gecko Moonveil Regent Mouth // Feed Mouth // Feed Myojin of Seeing Winds Nexus Mentality Night of the Flying Merfolk (playtest) Paradoxical Outcome Plagon, Lord of the Beach Pol Jamaar, Illusionist Regal Force Ribbons of the Reikai Riptide Director Sage's Reverie Scroll of Isildur Sea Gate Loremaster Shaman of the Great Hunt Shamanic Revelation Slate of Ancestry Soul of Ravnica Staff of Eden, Vault's Key Swordsman's Steel Tazeem The Horus Heresy The Spirit Oasis Tishana, Voice of Thunder Titan of Littjara Titan of Littjara Vivien's Stampede Voja, Jaws of the Conclave Volo, Itinerant Scholar Winged Portent

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
This is the case for the $200 MTG X Marvel Secret Lair add-on version
But we did, and they were a huge hit