Then when you swing you can flip it, but you don't have to
Yuffie isn't put onto the battlefield until the ability resolves
Dumping a lot of lands with this ability won't just put you ahead on mana, but also thins out your deck and makes it more likely that you draw the cards you need to win
Alternatively, you could spring for one of the two starter decks for this set: either the Amber/Ruby deck with Jim Hawkins and Tigger, or the Emerald/Sapphire deck starring Go Go Tomago and Gadget Hackwrench
You won't at all be surprised to hear and see that one of the first cards shown off from the set features Sephiroth coming down from the heavens, sword in hand, ready to stab you-know-who just offscreen, which is of course morbid as hell, but makes for some pretty great card art at the very least
For just and an added , you get Blizzard , which will let you return target creature to its owners hand