Is Heartfire Hero legal in Standard, Modern, and Commander?

Heartfire Hero is legal in: Modern, Legacy, Vintage, Commander. It is banned in: Standard, Pioneer.

Heartfire Hero

Q: What type of card is Heartfire Hero?

Heartfire Hero is a Creature — Mouse Soldier. Its oracle text reads: "Valiant — Whenever this creature becomes the target of a spell or ability you control for the first time each turn, put a +1/+1 counter on it. When this creature dies, it deals damage equal to its power to each opponent. Power/Toughness: 1/1"