You can Special Summon a high-level monster, like "Dark Magician", with "A Hero Emerges". But if your opponent selects a Special Summon-only monster like "Dark Necrofear", or a Spirit Monster, it is sent to the Graveyard.
When "Guardian Elma" is selected for "A Hero Emerges", and you have "Butterfly Dagger – Elma" on your side of the field, you can Special Summon her, but if you don't have it, then she is sent to the Graveyard.
You can activate "A Hero Emerges" even if you have only 1 card in your hand.