Your cards like Nissa, Vastwood Seer and Shrine of the Forsaken Gods are surely enabled, no matter how much mana was created first from creatures like Rattleclaw Mystic
The Spirits challenger deck is more white than most builds of Azorius Spirits decks right now, so Watcher of the Spheres and Empyrean Eagle are likely to hit the bench once you start upgrading, but are absolutely serviceable to start out
II, III - Brimstone - Add
We've seen two Secrets of Strixhaven cards with the ability so far: Arcane Omens and Archaic's Agony - both five mana Sorceries, both incredibly garbage
Zombies have plenty of intersection with the graveyard and ways to turn an army of tokens into a lethal task force
Giving the benefit of the doubt, they might have seen that number coming up, and saw that they planned a prejudice-related card, and combined them as a little joke