Oops!

Use Oops! to deal damage against enemies with: High value; Retaliate; Aloof; or who are engaged with another player. Engage with and attack another enemy with a lower Fight value (the ideal would be a Fight of 2, since it would be impossible to fail the attack by more than 2), without Retaliate, or who are not Aloof.

Do so without bonuses of s / icons, preferably using an attack with a natural Damage bonus (i.e. not one that depends on the attack being successful), and better still not using your investigator's better skill-values. Thus favourable choices (when available for the investigator's deck) are: Backstab; .32 Colt and Shrivelling [also Knuckleduster though this will result in the initial 'phoney' target doing its own Retaliate damage to you].

Since damage dealt by Oops! is not the result of an attack on the "target", failure now results in damaging the higher Fight-value enemy/bypassing its' Retaliate/avoiding risks of injuring another player already engaged with it.

This can be a directed tactic or merely to hedge bets facing multiple enemies. It is more practical cooperating with fellow players; and when your deck and/or that of a team-mate includes cards apt for bringing weaker and stronger enemies together and/or engaged with the attacker (e.g. Shortcut; "Let me handle this!"; On the Hunt; Taunt; Heroic Rescue).

Crispin · 4
For what it is worth, there also seems to be an interesting interaction between Fire Axe (which has a natural, resource-base damage bonus) and Oops. Still very situational since you could have used the 2 resources get +4 on your test vs main target. — Binoux · 27
The attack still counts as a failure, resolving effects approptitally. So you'd trigger retaliate and damage another investigatior, if the original attack targeted their enemy. — Django · 5164
Just retaliate; cannot be used except against an enemy engaged with you. But yeah. — CecilAlucardX · 10
Thanks, i didn't fully read the card before commenting. — Django · 5164
Thanks for pointing that out, I missed that too. — tylorlilley · 4
Carnevale of Horrors

Not a review or anything, but having mentioned this via the GutHub link at the bottom of the page, which seems to have gone unnoticed, I'll mention this here in the hope of correcting an error.

The encounter set included in Carnevale of Horrors, is actually called 'Carnevale of Horrors', not Venice as listed here on arkhamdb.

Guidance

This card actually says: You lose an action. Other investigator may take an additional action.

Well i don't know if this is good or bad card to include it to your deck. As a seeker in multiplayer you need every action to gather those clues so i'm kinda meh...

I am not a fan, myself. Maybe sometimes another investigator's action will be way more valuable than yours would have been (although, as you said, Seekers have some of the most efficient actions in the game), but so much so as to justify spending deck space on this? I don't think so. — CaiusDrewart · 3200
As a level 0 card, it can be included in non-seeker decks, which is probably its best use. However, the dunwich 'gators probably have cards they need more, and as Roland you can include better seeker cards anyway. I can't think of anyone else who can take it? — SGPrometheus · 849
Some seekers/builds are done for support. This gives you flexibility by allowing non-seekers extra time to fight/evade/pick locks. Roland can use it when there are no monsters around to let seekers nom clues. Lola can use it but I kinda see it less useful there. — CecilAlucardX · 10
Corner case: Use on any survivor with will to survive . Or on lola nova with 10+ actions and will to survive. lola + 3 seekers would give her 16 actions for 1 turn. — Django · 5164
I think it's a decent ability, just probably not worth a card slot. A higher-exp version might be worth it some day though. If it had 2 ?? icons, i could definitely see myself using it at 1 exp. — dr00 · 13
It's much worse than the above. It is you lose TWO actions, your friend gains ONE action. (ie, it is a virtual-action to draw the card). It's not a case of "is this every useful?", sometimes it will be, the question is "will this almost always be usefu — duke_loves_biscuits · 1285
Charon's Obol

I was extremely excited when I first saw this card. I thought I was going to immediately buy it in every Rogue deck I ever played. XP is incredibly powerful and fun in this game, after all. But the more I play with this card, the less I like it.

The odds that your character dies at some point in missions 2-7 of your campaign (if they die in mission 1 or mission 8, that's not really relevant for the Obol) are just way too high. Even if you run "I'm outta here!" and Cheat Death, I just think the risk is too great. Starting over midway through a campaign at 0 XP is a truly terrible feeling. In solo, maybe it doesn't feel quite so bad, but I really would not recommend this in multiplayer.

Note that "I'm outta here!" is far from a perfect failsafe here. Many scenarios don't have a resign space or have one that doesn't show up until the final Act. It won't save you then.

Moreover, Charon's Obol can also hurt you even if you don't die. This is because the Obol makes you play scared. Vastly increasing the consequences of dying makes it harder to play effectively. A very common situation in this game is the following: your investigator is severely hurt, down to 1 or 2 health or sanity remaining, but only a couple of turns away from a potential victory. What should you do? A normal investigator can go for the win. Sure, you might take a trauma, but that's not really a big deal at all. And you might win! With the Obol, you can't really do that any more. The consequences of defeat are too high to take otherwise profitable risks.

Furthermore, playing the Obol can force you to stuff your deck with durability cards (like the aforementioned "I'm outta here!" and Cheat Death), at the expense of better cards that actually help you win the scenario directly. This hurts your deck and can mean that your deck's power level isn't that much higher than a deck that doesn't run the Obol, but also doesn't have to run these cards.

Still, I can see the temptation here. If you like the thrill of risk and are OK with a strong chance of having to starting over, go ahead. But personally, I find the game much less fun when I'm running the Obol. And setting considerations of fun aside, if I were just trying to maximize my odds of winning the campaign, I do not think I would take it.

CaiusDrewart · 3200
What this card boils down to is this: Get an extra 13 xp over the course of a campaign. (5 if playing Night of the Zealot)(2 of that xp only counts if you carry the character over, so really 11/3) In exchange, tension is considerably higher, as every failed chaos pull or monster becomes magnified. If you like the tension, take it; if you don't like tension, then ask yourself if that 11 xp is worth all the stuff Caius listed above. — CecilAlucardX · 10
Check your math. The Obol is exceptional, so it costs 2 xp, and since you can't buy it until after the first mission, you only relevantly have it for 2-7 (if you don't carry over) in a campaign or just 2 in NotZ which makes it worth a net 10 xp in a campaign or a net 0 in NotZ. — Death by Chocolate · 1484
If you're forging your own path in TFA it will net you 14xp including the final scenario (12 that you can actually use without carrying it over). Unless my math is way off. There's two extra scenarios, and one scenario where it gets removed from your deck ahead of time, so you don't get the XP. — Zinjanthropus · 231
Suggestion

This card gets very broken with Sefina especially when combined with pickpocket lvl 2. One of the best combos we've found so far for it. Keeping elite enemies locked down whilst the team gets work done

Vicoforbes · 21
Certainly an effective combo, but given that 6 XP worth of cards are involved, I'm not sure it's fair to call it broken. But yes, I really like this for Sefina. — CaiusDrewart · 3200
Absolutely awesome with Sefina. Good with Akachi, though there's a lot of competition for her Arcane slots. Unconvincing for Skids and Jenny. — AndyB · 956
Why is it that good on Sefina? Just because she has 4 willpower? — QDI · 1
4 willpower and 4 agility. This adds willpower to the evasion check, so added to agility, it totals 8. — Lemmingrad · 21
But is it worth 4 XP? Cat Burglar and Elusive already provide guaranteed evasion and action compression to boot. — QDI · 1
Put that card in a Marie Lambeau deck and she gets a free evade action at 7 every turn as long as she has a doom on a card she controls. Like a Finn! — Ezhaeu · 51
this is probably a good way for Sefina to trigger win-by-2 type effects like Quick Thinking. Starting at 8 is already good, but Sefina also has access to others ways to boost agility and willpower. — Zinjanthropus · 231