This can definitely let an aggro deck get through for a big attack, even in the late game
When you're done, you have a single pile of face-down cards (assuming you have only one library)
And unlike Nevinyrral's Disk, you can't answer it by sitting there and building up your hand for a post-Disk smash or your mana base
Has an activated ability costing four generic mana and tapping, which allows you to Investigate. This mechanic creates a Clue token, an artifact you can later sacrifice with two generic mana to draw a card
6 Avacyn, Angel Of Hope Here To Save All The Permanents First Printed : Avacyn Restored (2012) The face of the last set of 2011 and 2012's Innistrad block, Avacyn, Angel of Hope is one of the most powerful Angel Creatures in Magic: The Gathering
Still, its not so amazing alone to make it essential