Are there any cards in Magic the Gathering that make an opponent loose life when they discard a card?

liliana's carress or megrim there is also Cruel ultimatum and Nichol Bolas, planeswalker which the opponent looses life at the same time as they either get milled and/or get milled

There are some enjoying cards that mill out your opponent's library: Ambassador Laquatus 1UU (3) mythical Creature — Merfolk Wizard (a million/3) 3: aim participant places the ultimate 3 enjoying cards of his or her library into his or her graveyard. Architects of Will 2UB(4) Artifact Creature — Human Wizard (3/3) whilst Architects of Will enters the battlefield, seem on the ultimate 3 enjoying cards of aim participant's library, then positioned them returned in any order. cycling (, Discard this card: Draw a card.) Archive capture 3UU(5) on the spot — capture If an opponent searched his or her library this turn, you will pay 0 extremely than pay Archive capture's mana fee. aim opponent places the ultimate 13 enjoying cards of his or her library into his or her graveyard. Glimpse the Unthinkable UB(2) Sorcery aim participant places the ultimate ten enjoying cards of his or her library into his or her graveyard. As you will discover, you're able to perform a little loopy milling in blue and black...

The two main cards of this type are Liliana's Caress (a enchantment for a black and a colorless mana that states "Whenever an opponent discards a card, that player loses 2 life.") and Megrim (an enchantment for a black and two colorless that states "Whenever an opponent discards a card, Megrim deals 2 damage to that player.")

Strictly speaking Liliana's caress and Megrim do what you want but if your trying to build a "discard deck" and looking for a card that will help with the killing you might consider The Rack. It deals damage to a player for not having cards in there hand and it only costs one colorless to cast. It used to be restricted i think but i don't think it is anymore, if someone slaps two racks on you and wrecks your hand with Hypnotic Specters and Hymn to Tourach's your in a bad way.

A little piece of advice when trying this strategy; don't focus so much on trying to stick in every card that will discard your opponents hand, that will happen on its own in part. Use good efficient creatures that are fast so your opponent has to use cards to deal with them; carnophage, sarcomancy, Nantuko Shades, and of course Hypnotic specter. Then your opponent will have to play removal spells, creatures, defensive enchantments, or die. Then use only very good discard cards and maybe four racks. The Rack will help you take advantage of the fast pace you set and your discard. I would stick to hymn to tourach, duress, hypnotic specters, and maybe one other four of, funeral charms aren't terrible and theres a great one I cant think of the name of. One Black; sorcery; target player reveals his/her hand, chose and discard a card from it. lose two life...something like that. I wouldn't go any further than that. Remember, when you draw discard and your opponent has no hand you just drew a dead card and consistently drawing dead cards is a real good way to lose the game.

Try lilianas cares

Yes.....