Is Sarevok's Tome legal in Standard, Modern, and Commander?

Sarevok's Tome is legal in: Legacy, Vintage, Commander.

What type of card is Sarevok's Tome?

Sarevok's Tome is an Artifact. Its oracle text reads: "When this artifact enters, you take the initiative. {T}: Add {C}. If you have the initiative, add {C}{C} instead. {3}, {T}: Exile cards from the top of your library until you exile a nonland card. You may cast that card without paying its mana cost. Activate only if you've completed a dungeon."

Sarevok's Tome

Artifact

When this artifact enters, you take the initiative.

: Add . If you have the initiative, add instead.

, : Exile cards from the top of your library until you exile a nonland card. You may cast that card without paying its mana cost. Activate only if you've completed a dungeon.