Mulligans
My idea is to hold onto Fel Reaver, Glacial Shard and Treachery (There are 2 of each to strengthen the odds of draw)
Use them on one turn to mill three opponents cards. Then on the next turn decimate his deck with low cost spells. There is enough warlock power in the rest of your deck to survive until the dastardly deed is preformed. It is a lot of fun and very nasty when accomplished.