Discard is typically black's main disruption tool however it is not exclusively black. As top lists for a card effects go this is one of the most eclectic I have done. With counterspells I found I was ranking the cards as a counterspell rather than rating the card so to speak. That felt appropriate in that list however due to the nature of discard effects suffering from poor scaling and diminishing returns after a point considering the whole card is much more relevant to them.
I was also expecting to have to talk about has been cards and B cubers so as to make the list up to ten but quickly found plenty of discard effects still in the main cube getting lots of love and doing good work. As such there is an honourable mentions section at the end for those that time has not been so kind to.
I card I associate both with old school formats like extended but also a card suitably balanced that it has seen countless reprints making it modern playable and periodically a standard card too. Duress is a very fair card, it is a preemptive Negate. For one mana you get pretty complete information, hopefully some options, a one for one trade and good proactive disruption. Eating a turn one Duress is still one of the worst things that can happen to most combo decks. It is pretty nasty for the control player too although Duress stays pretty good against them throughout the game.
The problem with Duress is that it sits dangerously close to being a hoser card. There are not a tonne of decks where I know I am keen to maindeck the Duress. It is usually a card I hedge with, I play it because I am already happy with the matchups where Duress isn't great but I am worried a bit about the ones where it will shine. There are a lot of creature heavy decks in the cube. Due to planeswalkers being so great almost all of these will have some Duress targets but the problem is that you don't have good odds on getting a hit, even on turn one, making Duress a bit dodgy. Even when you do get a hit in those matchups it is either a fairly irrelevant spell or something that wouldn't have effected the game for several turns. It is still more than fine when you only have one thing you can take, even if it isn't that great of a card. The information and going 1 for 1 is well worth the mana. Flat misses are a problem though. Discard already suffers from doing nothing on an empty hand, the fact that Duress can still do little on a full hand means you have to be quite careful how you build with Duress and where. Ideally I want to have reasons to play the card as well as ways to put it to use when casting it doesn't do anything.
9. Karn Liberated
Karn is not great discard at all. Usually you are doing that ability for the +4 loyalty and not the disruption or value. Seven mana Raven's Crime is pretty much the nut low for discard, even if it is exile and even if you can do it every turn! Karn is however a very potent card overall offering lots of off colour things to whoever wants them. Creature removal for green and blue, enchantment removal for black and red, hand disruption for the non-black decks etc. Karn solves problems and then sits there getting value every turn. Typically the discard is only that brutal in the slow control matchups which is not a surprise given that most other archetypes will be able to expend their hands or close the game before 7 mana planeswalkers enter the battlefield!
8. Wheel of Fortune
Like Karn Liberated this is a card you don't really play because it discards your opponents cards. Occasionally I play it because it discards mine but mostly I play it to draw me seven cards for three mana. Despite this, when I play with the Wheel, for whatever reason, I fairly frequently find myself casting it simply because of what I know or think it will get out of my opponents hand. Some games they have a Courser and you see what they draw, sometimes you hit them with a Gitaxian Probe and find out the horrors that await you. Most of the time you can make a pretty educated guess about what is coming at you if they don't play much. You might find you are only getting like +1 card on your opponent through casting a Wheel but based on what you know or assume about their cards combined with what you know about yours often makes it a great play. Nothing is more delightful than seeing a bunch of Thragtusk style cards go directly to the bin without bothering you at all, likely being replaced with elves and lands! Magic is more about quality than quantity, draw seven is great quantity and so the quality aspects of Wheel are often overlooked. Don't do this! Forcing someone to ditch a hand of gas is a winning move and a fantastic extra way to apply Wheel of Fortune.
7. Mind Twist
The ultimate in game ending plays. Land one of these on some one for X = 3 or more where the board is pretty even and it is really hard to lose. It is like the Strip Mine free win except that you don't need your opponent to be a little screwed. Despite this I am not all that into Mind Twist. It is much harder than you think being able to dump at least four mana into a spell that does nothing to the board without being very behind on said board. It is even harder to do this before your opponent has reduced their hand size to below three. Mind Twist has quite a narrow window in which to end the game. It has a slight wiff of Hidetsugu's Second Rite about it! Very powerful but not very fun to win with or lose to and not exactly a skillful card.
6. Inquisition of Kozilek
Very comparable to Duress but rather than be stronger or weaker depending on the matchup it is much more so based on the stage of the game. Early on an Inquisition will basically never miss, if it does you likely have a free win anyway because your opponent only has land and top end. As cube is one of the cheapest formats there is Inquisition does a bit better than Duress. It is the best anti-aggro discard spell. Late game it is pretty weak but most discard is anyway by that point. You want to be able to handle these late game dud draws within your build but it is generally worth the payoff. A turn one or even two Inquisition really puts you in the driver's seat for the game.
5. Vendillion Clique
A lot of the logic I used to describe how Wheel can be an effective discard tool applies directly to Clique. You never reduce their handsize with it but you can drastically reduce the quality of their hand. Clique obviously makes up for being card neutral discard by coming with a 3/1 flying flash body. You can also use it on yourself for a bit of bad looting should you need to. As such Clique is one of the best scaling discard effects being useful in at least one capacity at any given stage. Instant discard is also particularly nice as you can interact with all the card they draw as well. Just being instant pretty much removes all diminishing returns from a discard card and so clique is a real winner with its ever so useful body.
4. Kolghan's Command
While the discard is fairly limp on this card the way in which it is packaged has allowed for some very powerful and more creative uses for the card. I saw a great puzzle where you had to use the Command to discard one of your own things to pump up Tarmogoyfs for the win. As with Vendilion Clique the instant speed of the Command greatly improves the discard aspect. Kolghan's Command has some situational effects but the fact that you can land a draw step discard hit ensures the card gets a 2 for 1 most of the time while still doing the useful things you need it to do. Kolghan's is very similar to Cryptic Command in the way it gets value, controls a game and keeps you safe. The draw card option on Cryptic is a big part of that and is the equivalent of the discard on Kolghan's.
When you absolutely positively have to take the thing out of their hand, accept no substitute! While never better than Duress or Inquisition in the right situation Thoughtsieze is also never a dud. Against creature heavy decks you will hit the most relevant thing, against spell heavy decks the same applies as it does to top heavy ramp decks. For your two life you get reliability and that is most of the time the thing you want in your discard. It is incredibly well balanced, without the two life it would just be the Lightning Bolt of the discard spells with no reason ever not to pick and play it first. Two life actually hurts, as do lots of other things in the cube, friend and foe alike. You need to consider how much you can pay for things, if your deck is able to fight off aggression while spending its own life. Against a burn deck you are generally doing them a favour by casting this. If the reasons you are wanting to play Thoughtsieze are entirely covered by another discard spell that doesn't administer pain then consider that instead. In most of your matchups the two life isn't going to matter and at the same time, most of the matchups will also be ones in which Thoughtsieze outperforms other targetted discard effects which is why it remains the best and most played of them.
2. Hymn to Tourach
A nasty little spell that gives a cheap two for one as well as some really uncomfortable discard potential. As it is random it will be able to hit lands, including basics, which no other cheap discard does. Many a game has been won simply by landing a turn two Hymn on the two lands their opponent had in hand. It is functionally a Mind Twist with X=2 costed at BB instead of 2B. As such it does a lot of work in demonstrating quite how significant of a difference there is between a 2 drop and a 3 drop actually is. There are almost no 3 mana counterspells in the cube while the vast majority of the 2 mana ones are in the cube. The main weakness of getting card advantage through discard is tempo loss. Yes, that is also the main disadvantage to getting card advantage through drawing cards and yes, discard is also weakened by diminishing returns which card draw isn't, I am not comparing discard to card draw as a way towards card advantage, just stating the facts about cards in isolation. If you are getting card advantage out of discard effects then Hymn is the best of those because it costs you the least tempo. It is a fairly simple equation of cards per mana, you will find Ancestral Recall at the top of that list with Ancestral Visions and Treasure Cruise next in line, shockingly the best draw effects in the game! After that however you will find the Hymn sat atop the second highest level of efficiency.
Night's Whisper might do much the same for your card advantage situation for the mana and it wouldn't becomes useless as your opponent consumed their hand but that is entirely overlooking the disruption caused by discard. Even giving your opponent choices as to what they lose still has a significant disruptive effect most of the time. You choosing, even from a restricted selection of cards has a lot more disruptive capabilities and random can do worse still. On average random is probably the most effective but it is obviously more... random. As such sometimes it will be as weak as letting them chose. Hymn is a cheap two for one and it is disruption which isn't something you can easily find on other cheap card advantage cards.
1. Liliana of the Veil
As a discard tool Liliana is kind of weak yet she remains atop this list because the function of the card as a whole is so rounded and effective. The discard is sorcery, costs 3 mana to get online and only does one discard per turn of their choosing while also forcing you to discard. If you cast Liliana and use the +1 then at that point you are pretty much worse of than you would be casting dribble like Mind Rot in terms of immediate impact on the game. The two big factors that make Liliana substantially better than Mind Rot and company are that she stays in play and that she can Cruel Edict for -2 loyalty. The edict function just gives your card options and utility and is good in much the same way Kolghan's Command is good.
With Liliana staying in play and gaining loyalty to force both players to discard she is a serious threat to a lot of decks. Like Karn but under half the cost! With Lili you get both some guaranteed initial disruption as well as having a threat left in play that most decks need to deal with. There are also obvious perks like the ability to turn the self discard into a positive thing. Liliana typically is a tempo play even when you use the discard effect. As she represents quite an annoying threat she is generally quite a priority target. Four loyalty is a big chunk to get through, especially if it is early in the game. Due to the urgency of killing her there is often some inefficient plays made, my general experience of making a turn three Liliana is that it eats my opponents entire turn to deal with her if they are even able.
The honorable mentions section is rapidly growing as I do it but includes some fantastic cards. The first of which is Raven's Crime, the bane of control! One mana one for one discard isn't exciting when you gain little information from it and have no choice in what to take. Used on turn one it will hit the least relevant card and often have no impact on the game. Why Raven's Crime is so good is when you pair it with cards like Life from the Loam. Its ability to turn lands into useful spells in an ongoing way is difficult to disrupt and really hard to beat for any slower deck, even a deck that simply requires a certain mass of hand size to go off. You can only really play this in the most grind win orientated decks but it is an incredibly card economical way of beating and archetype. Often used with Worm Harvest as the win condition and Gifts Ungiven as a potent way to tutor for your land and graveyard abusing effects.
Transgress the Mind is a subtle card that has been the backup discard spell, the Ponder when you wanted Brainstorm, the Searing Spear because you didn't get Bolt. Transgress does what you need it to with a little bit of a perk at the cost of some clunkiness. It hits all the big scary things and has generally the broadest target range of the discard spells. The exile can be terrifying for some decks and just a pain for others. The biggest issue with Transgress is that is misses most of the countermagic out there making it the weakest of the options in a Duress role. You will play things like Distress and Addle over it and they are pretty weak. Where Transgress shines is in those "can't beat that" situations. Your opponent wants to cheese you with a Worship, don't just pull it from their hand but exile it and turn their cheeky Auramancer into a Grey Ogre.
I don't seem to be able to do an article without harping on about the wonders of Cabal Therapy. Now I do one where it could reasonably get some appraisal and I didn't even put it on the main list! As we have tended towards midrange things the quirky uses of Therapy have declined. Back in the day it was all about getting it in the bin with an Oath and then flashing it back to take their Force of Will while triggering your Academy Rector. Synergy has declined and power has increased, with that Cabal Therapy has taken hits. Less confidant players rarely take it and sensibly so. It is one of the hardest cards to use well in the cube. I can see it making a return but as a result of increased information from cards like Courser of Kruphix and Gitaxian Probe combined with more decently playable creatures you quite want to sacrifice appearing in black.
Therapy is a card I go on about and so is Death Cloud! Death Cloud has discard utility and so should appear on this list! You rarely play it specifically for the discard aspect. A symmetrical Mind Twist for BBBX does not a good spell make. The glorious thing about Death Cloud is how it reduces the overall resources in the game meaning that a small edge is relatively speaking quite a big one. Just having an annoying Bloodghast to recur can be game over if you wipe out their hand along with a bunch of lands. The discard aspect of Death Cloud works with the general theme of the card even when it isn't the specific part of the card you want to be using. Smallpox is much the same, for half the cost of Death Cloud you can play it with X fixed at one. Great if it misses one more of your things than your opponents and devastating if that is two things.
Ravenous Rats and Mesmeric Fiend were used a fair amount back in the day as disruption and value in Recurring Nightmare style rock decks. Now there is a bit too much removal for Fiend to shine and Rats simply isn't enough disruption to merit a 2 mana 1/1. Another discard creature that no longer see much love is the mighty Hypnotic Specter. This guy was the best value creature in all of magic for a very long time. Dark Ritual into Specter was good games unless they had the one mana burn or the Swords to Plowshares in hand. While still playable in the cube is it a bit too easy to kill and a bit expensive for 2/2 stats. Black has lots of quality in the three slot that is generally more useful in the roles they are needed for. Black is good against control which is where Specter shone most and so hasn't seen play since Vampire Nighthawk was printed. Even that doesn't see play now...
Finally we come to Blackmail, a surprisingly playable card in cube. Like Transgress it has always been a backup option when the better spells are gone but there really isn't that much redundancy in "targetted" one mana discard. Cube being so quick often means hand sizes are quickly diminished. I have played (on the draw obviously) Blackmail and had it be better than a Coercion (they had a land I could take!). Of all the one mana targetted discard Blackmail certainly scales the best into the game. The question is how close is it to Raven's Crime as a turn one play on the play? The answer isn't simple at all sadly. A lot depends on how good both players are and how much of a read the players have on each other. The short answer is that in general you get a reasonable amount of value over a Raven's Crime, both information and disruption, however there is a significant delay on the relevance of that disruption. You might take away their fourth land or their preferred three drop but that won't actually do anything for two or three turns which greatly reduces the value of Blackmail being one mana. Even costing two mana and not hitting one or two drops Transgress is more effective early game disruption than Blackmail. That said Blackmail is much more playable than it is generally given credit for and is a fun and skill intensive card to play with too.