In Alchemy Premier draft on a PC, played Elvish Elegy turn one in two consecutive games. Neither one did it mill. And then the card fizzled because it did not have any cards in graveyard. Later on, also had cards with entry that did not mill. Mysteriously, in a later game, I had Perennial Gravewarden come back to the battlefield. I did have it in my deck, but at the time did not have it in my graveyard. The conditions to bring it back were met (creature died and a creature entered). So not why that appeared.