Of note, only characters that have already been exerted are eligible to be challenged
You also need to make sure you hit your land drops, either with draw effects (Qiqirn Merchant and Adventurers Airship provide usable bodies as well as draw smoothing) or cards that directly give you lands or mana (World Map, landcyclers, Blitzball)
You may cast an instant or sorcery card exiled with this Saga, and mana of any type can be spent to cast that spell
Whether artificially boosting its counters with cheap spells or utilizing equipment to buff the legendary creature, Vivi can easily net you an absurdly high manabase to unleash plenty of powerful spells, or even melt your Magic: The Gathering opponents down on its own
Getting this out early will open strategy opportunities that would otherwise be unavailable to you until later in the game, giving you a great head start
Expect a flurry of frozen fun before the adventure heads into uncharted territory