Is Silumgar Assassin legal in Standard, Modern, and Commander?

Silumgar Assassin is legal in: Modern, Pioneer, Legacy, Vintage, Commander.

What type of card is Silumgar Assassin?

Silumgar Assassin is a Creature — Human Assassin. Its oracle text reads: "Creatures with power greater than this creature'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 this creature is turned face up, destroy target creature with power 3 or less an opponent controls."