Zoroark, the Illusionist

When Zoroark, the Illusionist enters the battlefield, search your library for a creature and exile it. Zoroark, the Illusionist becomes a copy of that creature until it is dealt damage. When Zoroark, the Illusionist leaves the battlefield, shuffle target exiled creature into your library.
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It doesn't just transform itself - it also has the power to make hundreds of people see its illusions.