This card is really fun and really good. Experience is immensely powerful in this game, and a multiplayer group that Delves aggressively can easily get about twice as much of it as a group that does not. A few tips for using Delve correctly:

1) With only a few exceptions (The Gathering and Extracurricular Activity come to mind), you don't want to Delve in the middle of the scenario. Even if there seems to be a quiet moment, Delving will rapidly make it unquiet, and this is no good. Rather, you want to Delve almost at the end of the scenario, right as the investigators are poised to win. If you're about to resign, to spend clues to advance the last Act card, or otherwise achieve the end of the scenario (and even when you're playing blind, it's very obvious when the scenario is about to end), that is the time to Delve. The majority of scenarios have a design that makes it possible for the investigators to hang around for a turn or two while on the cusp of victory.

This has numerous advantages. First and foremost, you don't have to deal with a lot of the encounter cards. Any monsters that show up can be ignored (although you might want to kill them if they're VP monsters), any damage/horror you take that doesn't kill you is irrelevant, etc. Moreover, since you have seen what the encounter cards in the scenario are (if you didn't know them already), you should know if Delving is safe or not. If there's an encounter card that might kill you or otherwise cost you the scenario, you can properly weigh the risks before Delving.

2) If there is a severely wounded investigator who cannot draw the extra encounter card without risking trauma, that investigator can sometimes resign before everyone else Delves. They don't have to draw the encounter card, and they still get the VP!

3) Cards like Ward of Protection, "Let me handle this!", etc., can make Delving at the end of the game considerably safer.

4) The other time to Delve is when you are certain to lose. If everything went wrong and you are inevitably going to have to resign in defeat or take trauma anyway--and we've all been in this situation--there's no reason not to get a VP or two first.

Played in this way, the drawback of Delve Too Deep is not really the encounter cards it draws, which hardly end up mattering at all, but just the fact that it takes up the spot of a card that could otherwise help you win the scenario. But the VP reward is more than enough to justify that, in my opinion. And you can of course replace it by the the last scenario or two.

If you haven't tried a multiplayer group in which every investigator packs two copies of Delve (use proxies to make this happen), I highly recommend it. Your decks will power up incredibly quickly.

Many people think this card is totally broken. Is it really? Let's analyze it.

Costs

• 5 XP: Very expensive, but reasonable for such a powerful effect. We're lucky it's not exceptional.
• 3 Ressources: Reasonable price, which most investigators should be able to pay. Only Dark Horse decks may find it too expensive.
• Relic Slot: Shares the slots with some other powerful cards, like Elder Sign Amulet, Holy Rosary or St. Hubert's Key. Most of these cards are mystic, so the slot is ok. Relic Hunter is also an option.

Requirements

In order to get the most out of this card, you need:

• In play as early as possible
• A reliable source of horror
• horror soaks to protect it

Getting the key into play

Only way to draw this card early is hard mulligan and seeker cards:

• Preposterous Sketches, but only for the person playing it. All others can be played on other people.
• Eureka!
• No Stone Unturned 0, No Stone Unturned 5
• Cryptic Research
• Eidetic Memory when copying one of these cards

Horror Sources

• Forbidden Knowledge
• Scrying 3
• Shrivelling, but very situational

• Painkillers, but only if there's damage on your investigator

• Most of these are cards. Other than these, enemies are the most reliable source of horror. But they often deal damage as well, so you need damage soaks (Bulletproof Vest) and/or healing (Strange Solution).
• To play it safe, stop taking horror intentionally after the second, so it it's bonus is only at +2. Then it won't leave play when you take another horror wihtout a soak.

Horror Soaks

• Neutral: Elder Sign Amulet is the best neutral soak, but it's also a relic and requires Relic Hunter in addition. Calling in Favors can be used to re-play an ally, healing him in the process.
• Guardian: Brother Xavier or any ally. Heal them with Inspiring Presence
• Seeker: Has Lot's of disposable allies like Art Student or Laboratory Assistant
• Mystic: Holy Rosary or any ally.
• Rogue: Several expensive allies. If possible use a different class or neutral cards.
• Survivor: After Cherished Keepsake, there's Peter Sylvestre 0 and Peter Sylvestre 2, the best horror soaks in the game.

Other things to note:

• When taking more than 1 horror, you can place any of them on Key of Ys
• This card can replace other boosters, like Spirit Athame or Dark Horse
• Direct horror can't be redirected, even when this card is in play.
• You can't use Agnes Bakers ability while this card is play, unless it's direct horror

Summary

This card is definately powerful, but uesless if you can't put any horror on it or it's destroyed. So i wouldn't put my first 5 XP into this card, unless your deck (or your party) is built around it.

A strong contender for most unplayable card in the game right now, at least if we're talking Hard/Expert. The upcoming Finn Edwards (who will have 4 Combat) may be able to use this card, especially since he will be very good at exhausting enemies first (which turns off Retaliate). But for Skids or Jenny, this is 100% unusable on anything but Easy, and even there it's unnecessarily dangerous and I would not recommend it. Obviously, Sefina can't even consider it.

(Update: Finn actually has 3 Combat. So I think this is pretty bad even for him.)

Although consistent +1 damage is one of the most desired traits in a weapon, the fact is that most enemies in this game don't have Retaliate. Given that Knuckleduster lacks a to-hit bonus, and that Rogues have low strength, using this card means subjecting yourself to a ton of unnecessary damage. You can evade and exhaust the enemy first to avoid this, but I really don't recommend this. Evading enemies and then fighting them is incredibly wasteful for any investigator not named Finn. Either just kill them or evade them, but don't waste actions doing both. Rogues have plenty of other weapons to pick over this.

This card continues a very weird trend in the design of Rogues where the class gets cards that don't remotely fit the investigators. Rogue weapons like Knuckleduster, Switchblade, and .41 Derringer all seem designed to work for investigators with really high strength. Except, you know, none of the Rogues actually have that, so Rogues are terrible with their own weapons. (In contrast, Survivor weapons like the Fire Axe and Baseball Bat are much more sensibly designed to work for low-strength investigators, so Survivors are actually good with them.)

Anyway, if you asked me to name the least useful card in the game right now, I think I might pick this one. Although, come to think of it, at least it doesn't cost 4 XP like the Springfield M1903 does. So maybe it's the only second-least useful card in the game. That's something.

This card can target any card in a players deck, including weaknesses. This aspects usefulness depends on the weakness in question:

• Some weakness do nothing, when drawn early: Abandoned and Alone, Shell Shock, Crisis of Identity
• Some are trivial when the party is spread out: Searching for Izzie, Smite the Wicked
• Some weaknesses need time before they can be solved, so it's important to draw them before the mid game: Hospital Debts, Cover Up, Baron Samedi, Angered Spirits
• Others require some preperation: Any enemy weakness, Overzealous, The King in Yellow, Final Rhapsody
• Some should be killed over and over for story reasons: spoiler

Other combos:

• Get powerful signature cards into play early: Green Man Medallion, Spirit-Speaker, Split the Angle
• Save deck space by including only 1 copy of unique or limited assets, like Lone Wolf, Dark Horse or Leo De Luca
• Can be copied wtih Eidetic Memory
• Gets better with more players, as the target card pool gets bigger and with that, solutions to challenges
• Can be played in any player window, including skill tests during mythos phase. This may save a player, as he could search his deck for the appropriate skill icons, like Guts against Rotting Remains

At the time of writing this had only been out a few days - and I've used it in 3 games...

This card is quietly awesome - if you, or a fellow investigator, have another card that you really need.

It's not flashy. It isn't fancy. There's no cool combos I can see. Letting someone draw any card from a deck doesn't seem that spectacular. But...

• your Guardian needs his Shotgun - fixed.
• Minh needs her Analytical Mind - no problem.
• Your mystic needs a Shrivelling right now, okay ... done.

No fuss, no worries about weaknesses or where it is in the deck, just for 2 resources take any card. It doesn't even cost you an action.

Okay, that is spectacular.

The down side is that 5 XP is a lot of XP. It's up against flashier cards, like the The Red-Gloved Man, Deciphered Reality, Strange Solution. And it's only as good as the card you need to grab, so it probably isn't a good pick for early in a campaign. However, later on, when you've a few high-value cards in the deck - this one is a solid choice.

(That said, for Minh Thi Phan, Analytical Mind is so central to her that I could imagine taking this early for her)

A really solid multiplayer pick.

Solo, it loses too much benefit to be worth it's XP, and Seekers have plenty of access to filtered draw through Old Book of Lore, Eureka!, and No Stone Unturned anyway.