Keening Stone 
Artifact
, 
: Target player mills X cards, where X is the number of cards in that player's graveyard.
Legality
standardNOT LEGALpioneerNOT LEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL
Artifact
, : Target player mills X cards, where X is the number of cards in that player's graveyard.