This is a complex and subtle control deck the I find a joy to play.  I was always a fan of discard decks with Megrim, but I had the consistent problem of losing after my opponent was reduced to top-decking, and couldn't discard any more.  This deck solves that problem.  First you want to get your opponent top-decking by any means necessary.  Use your Rats and Fiends early - the rats make great blockers; the fiends will quickly disrupt your opponent's early-game plans.  Finish off the hand with Mind Rot, Stupor, Mind Sludge, and the Specters.  Taking a turn out to play a Grimoire tends to work well, as it keeps you drawing land, which can otherwise be a little scarce.  Once your opponent's hand is empty, start in on the permanents in play.  Recoil is a fantastic late-game card, as it effectively destroys what you target after your opponent has no cards in the hand, as well as triggering half your enchantments and artifacts.  Pair Blizzard Specter with a specter's shroud or other Specter to do the same thing.  Wash Out is good in a pinch, and Sleeper's Robe will turn your Rats and Fiends into card-drawing power and one-damage irritants, so long as you keep your opponent's side of the field clear of pesky blockers.  An early Nihil Quest tends to be a deathblow in this deck.