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

Mist Dragon is legal in: Legacy, Vintage, Commander.

What type of card is Mist Dragon?

Mist Dragon is a Creature — Dragon. Its oracle text reads: "{0}: Mist Dragon gains flying. (This effect lasts indefinitely.){0}: Mist Dragon loses flying. (This effect lasts indefinitely.){3}{U}{U}: Mist Dragon phases out. (While it's phased out, it's treated as though it doesn't exist. It phases in before you untap during your next untap step.)"

Mist Dragon

Creature — Dragon

: Mist Dragon gains flying. (This effect lasts indefinitely.)<br>: Mist Dragon loses flying. (This effect lasts indefinitely.)<br>: Mist Dragon phases out. (While it's phased out, it's treated as though it doesn't exist. It phases in before you untap during your next untap step.)