This deck type is used to force your opponent to constantly move cards from his/her library to his graveyard. As we all know, if your opponent can't draw a card, he forfeits the game and declaring you the winner. You can find these types of cards in either blue or black, but I am going to just go through the good blue ones.
One enchantment I love to use for my Discard Deck is Jace's Erasure. This card states that any time you would draw a card, you may have target player put the top card of his/her library into their graveyard. Since you draw a card at the beginning of every one of your turns, you may force him to discard the top. With this in mind, your best bet would be to find quite a few instant and sorcery cards allowing you to draw cards, the more the better! Let's get to my personal favorite discard sorcery, Tome Scour. This card only cost 1 blue mana to play and it forces your opponent to put the top 5 cards of his/her library into their graveyard! That is a very small price to pay with a very good outcome. An instant card you must have is the Archive Trap. If an opponent searches his library in a turn, you may pay 0 to play it rather than pay its cost, and it forces that person to move the top 13 cards of their library to their graveyard! Although it is a very nice trap and would be awesome to set, I just go ahead and pay the 5 for its cost anyway just in case they never search their library.
You know as well as i do that you can only have up to 4 of the same card in your deck, well there is always a way around things like that! Cards like Call to Mind and Mnemonic Wall allow you to return instant and sorcery cards from your graveyard back into your hand. Being able to keep returning Archive Trap and Tome Scour to your hand puts some major pressure on your opponent.
Now, I only have one of these cards but all hell would break loose if i had 3 more! Echo Mage is a level up creature card, once you get him to lvl 4, you can pay 2 blue mana and tap him to copy a target instant or sorcery spell TWICE!!! Therefore, upon casting Archive Trap, I can pay the ability cost for Echo Mage to force my opponent to move the top 39 cards of his library to his graveyard.
Sword of Body and Mind is an artifact equipment with perfect qualities for a Discard Deck. First, the attached creature gets a +2/+2 and protection from green and blue. When the attached creature deals combat damage to a player, you put a 2/2 green wolf creature token on the battlefield and the player you dealt damage to, moves the top 10 cards of his library to his graveyard.
If you are ever lucky enough to get either of these cards, you must definitely put a Discard Deck together! Jace Beleren- Planeswalker ( the most important part, -10 to move top 20 cards of target players library to graveyard ) or Jace, the Mind Sculptor- Planeswalker ( -12 exile all cards from target players library then that player shuffles his hand, which becomes his new library )!!! to go from sooooo many cards to what they had in their hand as their library is just amazing!
