Scion of Halaster is a common Legendary Enchantment — Background card from Commander Legends: Battle for Baldur's Gate (CLB), collector number 498.
Commander creatures you own have "The first time you would draw a card each turn, instead look at the top two cards of your library. Put one of them into your graveyard and the other back on top of your library. Then draw a card."
All Commander Legends: Battle for Baldur's Gate cards and prices