If a substitute card enters a public zone (the battlefield, the graveyard, the stack, or exile unless it's exiled face down), use the actual double-faced card and set the substitute card aside

Akul the Unrepentant Ancestor Dragon Archive Dragon Armament Dragon Bahamut, Warden of Light Betor, Kin to All Bloomvine Regent Bonehoard Dracosaur Boulderborn Dragon Clarion Conqueror Decadent Dragon Dirgur Island Dragon Disruptive Stormbrood Dracosaur Auxiliary Dragon Mage Dragonfly Swarm Dragonhawk, Fate's Tempest Drakuseth, Maw of Flames Feral Deathgorger Fin Fang Foom Firespitter Whelp Hoarding Dragon Immersturm Predator Incinerator of the Guilty Jeskai Shrinekeeper Karakyk Guardian Kheru Goldkeeper Lathliss, Dragon Queen Lorehold, the Historian Magmatic Hellkite Malevolent Witchkite Marang River Regent Nebula Dragon Neriv, Heart of the Storm Niv-Mizzet, Guildpact Niv-Mizzet, Visionary North Wind Avatar Nova Hellkite Pet Avengers Prismari, the Inspiration Purging Stormbrood Quandrix, the Proof Ramos, Dragon Engine Ran and Shaw Rapacious Dragon Realm-Scorcher Hellkite Riling Dawnbreaker Runescale Stormbrood Sagu Wildling Savage Ventmaw Scavenger Regent Shiko, Paragon of the Way Shinryu, Transcendent Rival Shivan Dragon Silverquill, the Disputant Sonic Shrieker Spinerock Tyrant Steel Hellkite Stingerback Terror Stormscale Scion Stormshriek Feral Summon: Bahamut Terror of Mount Velus Terror of the Peaks Teval, Arbiter of Virtue Twinflame Tyrant Twinmaw Stormbrood Ureni, the Song Unending Whirlwing Stormbrood Witherbloom, the Balancer Yiazmat, Ultimate Mark

Her etb effect is good enough to carry the card on its own
It's done by preventing a dominant strategy from emerging
Children under 15 also are not normally able to acquire a My Number Card, so they wont be able to purchase items with that restriction either