Millstone

Oracle Text

2, T: Target player puts the top two cards of their library into their graveyard.

Card Rulings

10/4/2004 Can be used on a player with less than 2 cards in their library. It will remove 0 or 1 cards if that is all that is available.
10/4/2004 It is not a draw effect so it will not cause a player with less than 2 cards in their library to lose.
10/4/2004 Since you are putting more than one card in the graveyard at one time, the affected player can choose the order the 2 cards go in.