Is Shining Armor legal in Standard, Modern, and Commander?

Shining Armor is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Pauper, Historic.

Shining Armor

Q: What type of card is Shining Armor?

Shining Armor is an Artifact — Equipment. Its oracle text reads: "Flash When this Equipment enters, attach it to target Knight you control. Equipped creature gets +0/+2 and has vigilance. Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)"