Mysterious Tome // Chilling Chronicle

Commander is where Mysterious Tome // Chilling Chronicle has the most room to breathe — blue spellslinger decks, particularly those helmed by commanders that reward casting or copying instants and sorceries, can hit the flip threshold naturally by the mid-game. In Legacy and Vintage the card is legal but entirely absent from competitive lists; those formats move too fast for a three-mana do-nothing-immediately artifact. Modern and Pioneer offer more hospitable spell-heavy shells like Izzet tempo, but even there the setup cost competes poorly against cheaper, more immediate draw engines. Oathbreaker, which often runs higher spell density than Commander, is a plausible home if your signature spell is an instant or sorcery that benefits from being copied.