Is Belltoll Dragon legal in Standard, Modern, and Commander?

Belltoll Dragon is legal in: Modern, Pioneer, Legacy, Vintage, Commander.

What type of card is Belltoll Dragon?

Belltoll Dragon is a Creature — Dragon. Its oracle text reads: "Flying, hexproof Megamorph {5}{U}{U} (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, put a +1/+1 counter on each other Dragon creature you control."