Unfathomable review

Unfathomable understands that board games are infinitely better if they include some good old-fashioned backstabbing. Namely, it challenges a traitor in the group to ruin everyone else’s day. And by ruin, I mean “sink their boat and leave them at the mercy of gribbly monsters”. The result is one of the best cooperative board games I’ve played in a long time.

That isn’t unexpected, though. Because it’s an update to the excellent but now out-of-print Battlestar Galactica adaptation, Unfathomable was always going to be ‘good’. The question is, does it go above and beyond its inspiration?

What is it, and how does it work?

Essential info

Unfathomable cards, roles, and standee

(Image credit: Future)

– Game type: Co-op strategy
– Players: 3 – 6
– Difficulty: Moderate
– Lasts: 2 – 4 hrs
– Ages: 14+
– Price: $80 / £70
– Play if you enjoy: Arkham Horror, Betrayal at House on the Hill, Horrified

Set in the mists of 1912, Unfathomable begins mid-way through a cruise to Boston. Unfortunately for the ship’s passengers, this isn’t a relaxing experience. Storms soon roll in and mysterious ‘Deep Ones’ emerge from the waves, climbing aboard in the direction of something beneath the ocean. Oh, and a villainous ‘hybrid’ is trying to sabotage the vessel from within. 

This leaves us with one hell of a conflict. Most players are human, and they must reach port whilst fending off monsters that would very much like to eat them. Meanwhile, someone else controls a secret traitor that we have to assume is partial to passenger a la carte as well. But unlike other sabotage games such as Betrayal at House on the Hill, it’s impossible to know who’s who.

This sense of paranoia comes to a head at the end of each turn, where a crisis requires players to contribute numbered skill cards (strength, observation, will, lore, or influence) in secret that will help them meet a target. Add the right kind and you’ll reach that total in no time. Use the wrong ones and you might just fail. It’s an elegant concept that makes you question everything.

Unfathomable board setup

Mother Hydra and Father Dagon are always lurking somewhere in the Deep, ready to send forth their minions (Image credit: Future)

Which you’ll need to, by the way. Survival hinges on your ship’s resources, and most problems chip away at one or another. Because running out of any immediately ends the game (and you’re often forced to decide which resource you’d rather sacrifice to keep the vessel on-course), human players have to jealously protect them. 

This provides fertile ground for discussion as everyone tries to figure out each others’ motivations. Is your friend really trying to make the best of a bad situation, or are they quietly working against you? 

Is it any good?

Although the concept powering Unfathomable is straightforward, the scaffolding that holds it up is more complex. Specifically, there are a lot of systems to learn. As with horror epics like Nemesis: Lockdown, this is both a blessing and a curse. The immediate downside? Setup, play, and packing away takes a very long time. To be precise, most sessions I ran lasted four hours or more. Much of this can be put down to me checking rules as I went, but even so, there’s no denying that the game is long-winded. Which isn’t a bad thing, of course. It’s just worth bearing in mind.

Unfathomable board and miniatures

This is probably what you’d call ‘being screwed’ (Image credit: Future)

However, there is a silver lining: namely, a long-lasting game you can truly sink your teeth into. Regular groups will get the most out of its thoughtful mechanics, and there are enough crises on offer that you won’t get bored if you’re making lots of return visits. This is the sort of game that demands dedication, but the payoff is top-tier.

When combined with randomized monster actions that cause domino effects of a kind usually seen in the Pandemic board game, Unfathomable is firing on all cylinders. Do you save those cornered passengers even though you might then be attacked and put out of action? Or is it better to abandon them so you’re still at your best for whatever happens next turn? There isn’t a right answer – it’s all just shades of gray.

Is your friend really trying to make the best of a bad situation, or are they quietly working against you?

The crisis system only adds to that unease. Because you can’t be sure who contributed what cards to the pile (and random cards from the deck are added anyway for extra uncertainty), it’s a tense experience that can make the hairs on the back of your neck stand on end. There’s nothing quite like realizing that someone is trying to cause your probably-unpleasant demise.

This is complemented by the tangible urgency driving gameplay. Your limit of two actions per turn ensures that you’ll never have enough time to do what you want, and the fact that you can’t collect items or fix damage without letting more immediate problems fester ramps up suspicion about where your loyalties lie. That can lead to frustration at the game’s stop-start nature, but it also conveys those overwhelming odds beautifully.

Other Arkham Horror games

Arkham Horror Files logo

(Image credit: Fantasy Flight)

Unfathomable is just one part of the Arkham Horror Files universe. You can check out other chapters with the links below.

Arkham Horror (Third Edition) (opens in new tab)
Arkham Horror: The Card Game (Revised) (opens in new tab)
Eldritch Horror (opens in new tab)
Arkham Horror: Final Hour (opens in new tab)
Mansions of Madness (Second Edition) (opens in new tab)
Elder Sign (opens in new tab)

Especially when the Captain and Keeper of the Tome get involved. These are special roles decided by a hierarchy from Unfathomable’s rulebook, and players are often given a choice between two secret outcomes (where the ship should go next or which spell to cast, for instance). Some are inefficient but safe, while others are dangerous yet lucrative. Seeing as you aren’t allowed to show anyone else which option you rejected, they’ll have to take your word that you aren’t screwing them over by choosing the worst possible path. Which you might be, of course. It’s like a horror movie in that things can quickly go from ‘bad’ to ‘oh god’.

Not that traitors have to rely on skullduggery alone. If you’d prefer to cause chaos, you can out yourself at any time. And unlike other hidden-role games, there’s a genuine benefit in doing so. Even though you’ll lose the ability to contribute more than one skill card to a crisis, you can take the fight directly to your opponents instead. You’re also allowed to trade your skills for unique traitor cards that will wreak havoc on the foe. It’s very fun in a “cackling maniacally” sort of way.

This does highlight the game’s biggest problems, though. First off, all these systems result in rules overload. Unfathomable is made up of many different moving parts, and a good deal of practice is needed to learn them properly. They compliment each other brilliantly, but getting your head around them is an intimidating task.

Unfathomable miniatures and cards closeup

Crises often challenge you to beat a score using different kinds of skill card (Image credit: Future)

In much the same way, this complexity causes the runtime to balloon. As an example, humans must reach a ‘travel score’ of 12 to win by collecting specific numbered cards after they’ve advanced far enough along a separate travel track. But because each of these travel cards only lets you progress in small bursts (usually between values of two and four), things start to drag. It’ll take players multiple turns to earn even three points of movement, so this is definitely a long-haul trip.

Luckily, the theming of Unfathomable gives you plenty to admire during that journey. As an Arkham Horror tie-in (putting it shoulder to shoulder with Mansions of Madness and Arkham Horror: Final Hour), this game’s art-deco style is shot through with a moody grittiness that puts you on edge from the start.

Its miniatures – of which there are many – are similarly evocative. It would have been nice to get more variety from the Deep One grunts, but their overlords are beautifully rendered. Make no mistake, these are showstopper monsters that dominate the board.

This is an intricate and superbly well thought-out setting

Still, Unfathomable’s world-building takes the cake. This is an intricate and superbly well-thought-out setting, and the backstory for each character immerses you in the narrative right away. Indeed, that was commented on the most during my playtests – thanks to a fully fleshed-out past with intriguing plot hooks, unresolved issues, and motivation aplenty for fighting or aiding the Deep Ones, I was much more invested in the heroes’ story than I’d anticipated.

Not that it’s all po-faced seriousness. Along with cheeky nods to Battlestar Galactica (namely a dog companion called ‘Starbuck’), there’s an amusingly off-kilter juxtaposition to some crisis cards. Why on earth would anyone be checking tickets during a monster attack, for instance? Our sessions left us with plenty of amusing anecdotes like this one.

Overall – should you buy Unfathomable?

If you’re in the market for great co-op board games for adults, it doesn’t get much better than this. While you’ll need to dedicate time to learning its systems, Unfathomable is a robust addition to the Arkham Horror franchise that should find its way onto fans’ shelves. It also has longevity to spare thanks to its many overlapping systems – just make sure you leave plenty of time to play.

The Verdict


4.5 out of 5


Unfathomable improves on a classic formula with fantastic world-building, tense mechanics, and enough tactical depth to keep you bewitched despite its long run-time.

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