Great Hall of the Biblioplex [Secrets of Strixhaven Promos]

T: Add C.

T, Pay 1 life: Add one mana of any color. Spend this mana only to cast an instant or sorcery spell.

5: If this land isn't a creature, it becomes a 2/4 Wizard creature with "Whenever you cast an instant or sorcery spell, this creature gets +1/+0 until end of turn." It's still a land.