This card is a perfect example of how a treachery can shape the entire campaign. Dunwich has many cards that force you to discard undrawn cards, and although this can normally be bad enough (especially if it pushes cards you need into the discard pile) this card makes it a punishing, deadly mechanic if not built for.
Anyone playing Dunwich needs to build their deck with this card specifically in mind. There are several counter options for it, though some investigators really have no counter and should not be picked for Dunwich because of that.
For All
-Consider resigning if running low and this is up. It is better to fail the scenario than take trauma, most times. This card gives you plenty of warning that it is going to kill you.
Survivor (can deal with this card)
-Devil's luck: Straight out cancels the card if you can't counter it by other means.
-Alter Fate: Get rid of the card from yours/an investigator's play area.
Rogue (will probably die from it)
-No easy counter. Either tank it, run versatile with Deny Existence (keep in mind the extra cards you pick for versatile should have draw on them or you're going to run into deck dilution easily), or dump points into Cheat Death.
Guardian (will probably eat this but be fine)
-No easy counter, but can stack a ton of mitigation to take the hit (I've had worse, just straight out tanking it, etc). Also guardians tend to have slower draw and even with the forced discards the event probably won't trigger.
Seeker (no direct counter but can probably cancel this)
-usually very squishy and can't survive the hit once it goes off and also cycle their deck fairly rapidly. They are definitely at a higher risk from this card. However with abilities like Forewarning they can cancel it. Many of them also have access to the mystic card pool, in which case Deny existence or Quantum Flux can help tremendously.
Mystic (makes this card their bitch)
-Having a high amount of cancels, deny existence (especially level 5), slow draw and quantum flux, this class is not in the least bit concerned by this card.
TLDR
If your character can pull from the level 1 survivor pool or any cards from the mystic pool, they will likely be just fine. If they cannot, consider versatile for deny existence.