Is Millstone legal in Standard, Modern, and Commander?

Millstone is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Historic.

What type of card is Millstone?

Millstone is an Artifact. Its oracle text reads: "{2}, {T}: Target player mills two cards."

Artifact

, : Target player mills two cards.

Set Antiquities

Rarity Uncommon

Artist Kaja Foglio

Artifact Modern Pioneer Commander