Is Knight of Valor legal in Standard, Modern, and Commander?

Knight of Valor is legal in: Legacy, Vintage, Commander, Pauper.

Knight of Valor

Q: What type of card is Knight of Valor?

Knight of Valor is a Creature — Human Knight. Its oracle text reads: "Flanking (Whenever a creature without flanking blocks this creature, the blocking creature gets -1/-1 until end of turn.){1}{W}: Each creature without flanking blocking Knight of Valor gets -1/-1 until end of turn. Activate only once each turn."

Creature — Human Knight

Flanking (Whenever a creature without flanking blocks this creature, the blocking creature gets -1/-1 until end of turn.)<br>: Each creature without flanking blocking Knight of Valor gets -1/-1 until end of turn. Activate only once each turn.