Using Nymph's Tears, you can turn Bone Pillars into Grey Nymphs without departing from our accepted definition of mono-Water. There's nothing about simply having Bone Pillars in your deck that makes it anything other than Mono-water, because the decklist has no Death cards in it.
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And no, it sucks for FG farming. Non-creature creature control (Plague, Rof, EE, etc.) just kills it, and if you don't get the Aflatoxin out fast, Otys kill it, too.