When it attacks, you reveal the top card of your library, put it in your hand, and lose life equal to its mana value ala Dark Confidant and Keen Duelist
Consequently, the probe was banned in Modern and Legacy, as well as becoming Restricted in Vintage
It is possible, however, and even quite effective, if you bring the right commander along
(Don't lay your noncreatures out at this point unless they're cards you are planning to play as soon as you have that much manafor example, you will generally cast a Pouncing Lynx on turn two, whereas Divine Arrow isn't usually a turn-two play.) A good "mana curve" of creatures is crucial to a successful Sealed deck
Yamatos character remains popular in the fan community
Consequently, Spell Snare has a boatload of targets in virtually every matchup