There are now several planeswalkers that want to make an opponent discard cards (e.g. Angrath, Davriel, Kaya, Liliana, and Nicol Bolas), which means we want to find spells that reward us for our opponent discarding. The most basic idea is to simply hit our opponent’s life total every time they discard a card, and there are a few cards that will allow us to do just that.
The original version of this idea was Megrim from Stronghold. For three mana, we do 2 damage to our opponent each time they discard a card. This seems to have set the standard that a discarded card is worth 2 life, which continues up to today.
Megrim was all there was until Magic 2011, when Liliana’s Caress was printed. This looks like a strict upgrade rendering Megrim obsolete: now we can do the same damage for only two mana. But do notice that the wording is slightly different. On the one hand, the opponent just loses the two life (it’s not damage, which might be prevented or redirected). On the other hand, in Magic there is always the possibility that some card interaction would want the enchantment to ‘deal damage’, so I think we can’t quite toss Megrim onto the scrapheap. (And, of course, for the purposes of Planeswalker Jousting, only Liliana gets access to Liliana’s Caress.)
A recent upgrade to Liliana’s Caress is Raiders’ Wake from Ixalan, but we should note that it also costs twice as much—we’re paying for that upgrade! Still, this card has its own discarding engine, making it possible to force a discard every turn, without having to rely solely on instants & sorceries or specters that need to also deal damage to force the discard. If our deck can wait until turn four for this, then this would seem to be the best option.
One specter with a built-in discard engine that also does the work of a Megrim is Scythe Specter, but it’s even pricier (3X the cost of Liliana’s Caress). On the upside, the potential damage is even greater—if they discard a 5-drop, they are taking 5 damage rather than 2. We also did 4 damage during combat! The obvious downsides, though, are that we have to do combat damage to cause any life loss (this card does not work with a simple discard spell like Duress), and creatures are always a bit more fragile on the battlefield than enchantments. Still, this might make a nice finisher in a discard damage deck.
Another creature with this discard damage ability is Fell Specter. It’s the same price as Raiders’ Wake, and it does cause an immediate discard when it enters the battlefield. Unlike most specters, though, it does not have the repeatable discard engine (“Whenever [Specter] deals damage to a player, that player discards a card.”) Overall, I would rate it below Raiders’ Wake, which I would have to objectively rate below Liliana’s Caress just for its mana efficiency (with the caveat that ratings of Magic cards are always subjective, depending on the needs of a particular deck).
One other enchantment that can reward us for making our opponent discard is Quest for the Nihil Stone. It’s cheap, but it does come with some other hoops to jump through. Still, the payoff is 5 life lost (a quarter of their starting health) per turn if we can get our discard engine going. Again, this might serve as a decent finisher in a discard damage deck.
CONCLUSION: Nothing is technically obsolete here, but it does seem that we might want to think twice before using Megrim. If we can’t play Liliana’s Caress because of deck-building constraints, or we happen to be playing other cards that want Megrim’s particular wording, or one extra mana would stretch our resources too much, then it might still have a place in some deck.