Mist Dragon [Mirage] Zombie Assassin how would I know it

how would I know it worked

Set: Shadows over Innistrad Type: Basic Land — Forest Rarity: Common ({T}: Add {G}

"Unworthy of consecration

you may return Genju of the Cedars from your graveyard to your hand

Set: Magic Origins Type: Sorcery Rarity: Mythic Cost: {2}{U} Each player shuffles their hand and graveyard into their library

Mist Dragon [Mirage] Zombie Assassin how would I know itSet: Mirage Type: Creature Dragon Rarity: Rare Cost: {4}{U}{U} {0}: Mist Dragon gains flying. (This effect lasts indefinitely.) {0}: Mist Dragon loses flying. (This effect lasts indefinitely.) {3}{U}{U}: Mist Dragon phases out. (While it's phased out, it's treated as though it doesn't exist. It phases in before you untap during your next untap step.) "Across the plains, farmers who braved the mists began to vanish. Most blamed the goblins; none