Shrine of Limitless Power
New Phyrexia — uncommon
Artifact
Shrine of Limitless Power rulings:
2011-06-01: Unlike most abilities that force a player to discard cards, this ability may be activated whenever you could cast an instant, including during your opponent’s draw step after they have drawn a card.
2011-06-01: You can’t force an opponent to discard a card they cast by activating the last ability in response. The spell is on the stack by then.