Is Sky Diamond legal in Standard, Modern, and Commander?

Sky Diamond is legal in: Legacy, Vintage, Commander, Pauper.

What type of card is Sky Diamond?

Sky Diamond is an Artifact. Its oracle text reads: "Sky Diamond enters tapped.{T}: Add {U}."

Artifact

Sky Diamond enters tapped.<br>: Add .

Set Mirage

Rarity Uncommon

Artist D. Alexander Gregory

Artifact Commander Pauper Legacy