By leaning on Zombie Infestation to feed your graveyard with discards, you can begin the engine by generating a steady stream of tokens. Queen Allenal of Ruadach cleverly upgrades this payload by turning every single token creation event into both your original Zombie and an extra Soldier token, giving you extra fodder to work with. Ashnod's Altar promptly harvests those creatures for colorless mana to keep the loop going, while Tresserhorn's Lord, Returned ensures that every single one of those required sacrifices instantly replaces itself by drawing you a card.