Is Knight of the Mists legal in Standard, Modern, and Commander?

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

Knight of the Mists

Q: What type of card is Knight of the Mists?

Knight of the Mists 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.)When Knight of the Mists enters, you may pay {U}. If you don't, destroy target Knight and it can't be regenerated."

Creature — Human Knight

Flanking (Whenever a creature without flanking blocks this creature, the blocking creature gets -1/-1 until end of turn.)<br>When Knight of the Mists enters, you may pay . If you don't, destroy target Knight and it can't be regenerated.

Set Visions

Rarity Common

Artist Harold McNeill