Mirage Block introduced a four-card cycle of "topdeck tutors" (and left everyone wondering where the red one was). The blue one and the black one are both banned in Legacy, the white was used to be banned but was eventually set free, and the green one was never banned but is no slouch. They set the standard for "tutor" cards that help you find something in your library and put it on top. Since these tutors arrived, few other cards in that category have been able to establish themselves. Some of the imitators offer additional benefits, but they cost two mana and are generally not worth it. So while Enlightened Tutor, Mystical Tutor, Vampiric Tutor, and Worldly Tutor are powerful and respected, two-mana stuff that lets you choose your own topdecks are generally fodder for scrubs. All except one... It doesn't take much life to find a card you need with this thing, especially if you have four copies of the card in question. But going through your library in five-card clumps, you're very likely to hit not just one card that you care about, but two or even three. When it comes to deck manipulation utility, almost nothing else comes close. You can get the pinpoint precision of Vampiric Tutor, the scorched earth total control of Doomsday, or the sky-high probability of unparalleled value offered by Lim-Dûl's Vault.