Silumgar Assassin [Dragons of Tarkir Pre-Release]
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Creatures with power greater than Silumgar Assassin's power can't block it.
Megamorph {2}{B}
(You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.)
When Silumgar Assassin is turned face up, destroy target creature with power 3 or less an opponent controls.