Mourn the Ancients

Destroy all creatures. For each creature you
controlled that was destroyed in this way, search
your library for a historic card, reveal it, and put
it into your hand. Shuffle your library afterward.
(Artifacts, legendaries, and Sagas are historic.)
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Generations ago, a sorrowing few forged the greatest
weapons history had ever known from the bones of
Ravnica's massacred elder dragons.