Is Sivriss, Nightmare Speaker legal in Standard, Modern, and Commander?

Sivriss, Nightmare Speaker is legal in: Legacy, Vintage, Commander.

Sivriss, Nightmare Speaker

Q: What type of card is Sivriss, Nightmare Speaker?

Sivriss, Nightmare Speaker is a Legendary Creature — Snake Cleric Warlock. Its oracle text reads: "{T}, Sacrifice another creature or an artifact: For each opponent, you mill a card, then return that card from your graveyard to your hand unless that player pays 3 life. (To mill a card, put the top card of your library into your graveyard.) Choose a Background (You can have a Background as a second commander.)"

Legendary Creature — Snake Cleric Warlock

, Sacrifice another creature or an artifact: For each opponent, you mill a card, then return that card from your graveyard to your hand unless that player pays 3 life. (To mill a card, put the top card of your library into your graveyard.)