Is Zhalfirin Commander legal in Standard, Modern, and Commander?

Zhalfirin Commander is legal in: Modern, Legacy, Vintage, Commander.

Zhalfirin Commander

Q: What type of card is Zhalfirin Commander?

Zhalfirin Commander 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}{W}: Target Knight creature gets +1/+1 until end of turn."

Creature — Human Knight

Flanking (Whenever a creature without flanking blocks this creature, the blocking creature gets -1/-1 until end of turn.)<br>: Target Knight creature gets +1/+1 until end of turn.