Tome Scour

Five cards off the top of a library for a single blue mana, with no body, no recursion, and no rider attached. The rate is the whole question every mill deck has to answer: at this efficiency, the math says you need roughly a dozen copies of effects this size to empty a standard sixty-card library, which is why a card like this only ever functions as one cog in a dedicated mill engine rather than a clock you can build around casually. Its usefulness as a baseline comes from precisely that absence of extra text. It is the cleanest possible statement of mill-per-mana, and decks that want to win by deck-out treat it as a unit of measurement: anything that mills more for the same cost is upgrade, anything less is filler. Pointing it at yourself is the secondary use that keeps it from being purely a one-trick spell, feeding graveyard strategies that want fuel in the yard rather than damage to an opponent's library. That dual targeting (the spell never specifies an opponent) is the small flexibility a one-mana sorcery this narrow can offer. Against unbounded card advantage or any library small enough to threaten on its own, it participates in a strategy rather than threatening anything in isolation, and that has always been the honest ceiling for a spell that buys exactly five cards and stops.