Is Heir to Dragonfire legal in Standard, Modern, and Commander?

Heir to Dragonfire is legal in: Historic.

What type of card is Heir to Dragonfire?

Heir to Dragonfire is a Creature — Human Warlock. Its oracle text reads: "{R}: Heir to Dragonfire gets +1/+0 until end of turn. {2}{R}, Reveal Heir to Dragonfire from your hand: Heir to Dragonfire perpetually becomes a Dragon, gets +3/+3, and gains flying. Power/Toughness: 2/2"