Wicker Man theory says you should always give opponents in your games a dilemna. They must not ever ignore you as a threat and they must be given a reason not to attack you.
Grimoire thief fulfils one of those roles being a major threat – milling an opponent’s deck and having the opportunity to use those removed cards to counter spells.
Image: http://resources.wizards.com/Magic/Cards/MOR/EN/Card152870.jpg
Set: Morningtide
Availability: Rare