Wall of Lost Thoughts 
Creature — Wall
Defender (This creature can't attack.) When this creature enters, target player mills four cards. (They put the top four cards of their library into their graveyard.)
Legality
standardNOT LEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL