Is Reito Sentinel legal in Standard, Modern, and Commander?

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

Reito Sentinel

Q: What type of card is Reito Sentinel?

Reito Sentinel is an Artifact Creature — Construct. Its oracle text reads: "Defender When this creature enters, target player mills three cards. (They put the top three cards of their library into their graveyard.) {3}: Put target card from a graveyard on the bottom of its owner's library."