Sifter Wurm

Trample
When Sifter Wurm enters, scry 3, then reveal the top card of your library. You gain life equal to that card's mana value.

"Rhonas's monument belongs to the wurms now. Look elsewhere for refuge."
—Arnun, vizier of the menagerie

Commander Legends

Trample
When Sifter Wurm enters the battlefield, scry 3, then reveal the top card of your library. You gain life equal to that card's converted mana cost.

Amonkhet Remastered

Hour of Devastation

For cards in your library with {X} in their mana costs, X is considered to be 0.

Once Sifter Wurm's triggered ability begins to resolve, no player may take other actions until it's done. Notably, opponents can't try to change your library after you scry but before you reveal the top card of your library.