Great Hall of the Biblioplex

Legal in Standard, Pioneer, Modern, Legacy, Vintage, Commander

{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.