Corridor Creeper: A Case Study in the Pitfalls of Predictions

Less than one week into the Kobolds and Catacombs expansion, a single, Neutral epic is taking the metagame by storm. From day one of the Trinity Series Live Finals, Corridor Creeper, a card that was written off in most pre-release card reviews, has proven to be a powerhouse card from the set.

Well-known for their innovative deck building and refinement, players from Team LUL abused other teams’ low-expectations for the giant worm and gleefully jammed the card into each of their nine decks. Immediately, other teams in the tournament caught on and, thanks to the option to resubmit decks, began replicating Team LUL’s strategy. The result was a tournament metagame that was infested with Corridor Creepers. Shortly thereafter, both the Standard and Wild ladders were completely contaminated with worms.

With its now obvious potency, how is it then that so much of the community, including professional players (Team LUL notwithstanding), were so far off the mark with their assessment of the card? After pouring over the numerous pre-release set reviews for Kobolds and Catacombs, it seems that most believed the card would be unremarkable. In some cases, even teams of experts not only overlooked it’s potential but also dismissed it as nothing more than a pack-filler.

Personal Failure


Admittedly, I was just as quick to disregard this card upon its reveal. Sure, the effect is nice, but a seven-mana 5/5 could never see competitive play, right?

Even when a fellow writer in the Hearthstone Top Decks Discord mentioned that he saw some potential in the purple worm, I had my doubts. Quickly, I responded with something to the effect of “Sure, seems like a good arena card.” while silently scoffing at the possibility Corridor Creeper making its way into ranked play. [Author’s Note: This is typically the self-satisfying, cop-out response I reserve for situations where I’m “politely” suggesting someone is overrating a card.]

Regardless, I certainly missed the marked on Corridor Creeper just as badly as the vast majority of Hearthstone players.

What’s the Point?

The point of this article isn’t to shame those (myself, included) who overlooked the power of a single card in a 135-card expansion. Nor is it to suggest that pre-release set reviews have no value. In fact, I’m just as guilty of hopping on the hype train in picking my Top 5 Kobolds and Catacombs cards for the Wild Hearthstone format.

Rather, it’s to look at how and why the vast majority of a community, even those regarded as experts, could so be so wrong in many of their predictions.

First Impressions

Sleepy Dragon

At first glance, there is nothing exceptional about Corridor Creeper. It’s a Neutral minion with a poor statline to mana cost ratio and, as it turns out, a very exploitable effect. While artist Nick Southham did phenomenal work, even the subject of the card’s art is rather grotesque and begs to be ignored. All of these factors contribute to a situation in which it is understandable that players would overlook Corridor Creeper.

By the Numbers

In Hearthstone card evaluation, the first assessment is always whether a card stands up to the Vanilla Test. For those unfamiliar, the Vanilla Test is simply an analysis of the numbers on the card (Mana Cost, Attack, and Health). Players look at a minion’s statline and compare it to a minion of the same cost with no text. For instance, the standard for a four-cost minion has long been Chillwind Yeti and two-drops better offer something more than a River Crocolisk.

Unfortunately for its pre-release ratings, Corridor Creeper fails the Vanilla Test miserably. At seven mana, a quick comparison can be made to War Golem. While this Basic minion is a strictly worse Dr. Boom, it still manages four more total stats than Corridor Creeper.

Obviously, nobody is paying seven mana for Corridor Creeper, but when a card is so far behind an already bad vanilla minion, it’s easy to pass up.

Set Neutrality

Aside from the sheerly unremarkable numbers on the card, Corridor Creeper was at a disadvantage being a Neutral minion. Synergistic mechanics and hero identities make class cards far more compelling than Neturals. This left Corridor Creeper drowning in a sea of very forgettable cards dumped the week of expansion release.

Likewise, in a set driven by the new Recruit keyword and Legendary Weapons, why would players waste time on another Neutral card? Yeah, it has the Beast tag, but so do several others from the set that will never see high-level constructed play.

Certainly Not Turning Any Heads

Finally, even the artwork makes Corridor Creeper easy to overlook. Reminiscent of a monster from Stranger Things, it becomes unsettling to look at the card for too long. The point being, this repulsive worm isn’t going to get nearly as many second looks as something as adorable as Snowflipper Penguin or as spectacular as Vulgar Homunculus.

Doomed to Dismission

All of these factors contribute to a first impression of Corridor Creeper that makes it easy to dismiss at a quick glance. Unfortunately, we humans have a tough time moving beyond our first impressions.

The result, in this case, was many players not giving this card the closer analysis it needed to be evaluated properly. It took careful consideration (and likely in-game playtesting) to figure out that, in a metagame dominated by minion combat, Corridor Creeper was rarely going to cost more than three mana.

Worse yet, even those that did revisit the card in-depth fell victim to the human tendency to shape their future assessments based on their early impressions. As such, it was likely that many wrote off Corridor Creeper’s card text as too slow or too difficult to abuse. Doing so only confirmed early inclinations of the card as unplayable. Obviously, this stance could not be any more false, but such conclusions are, at least, understandable.

The Fallibility of Professionals

With hobbyist players, it’s easy to understand whiffing on a sleeper card like Corridor Creeper. Surely, us casuals simply don’t know any better.

How is it, though, that professional players who dedicate hours of their day to Hearthstone could miss the mark so horribly on this card?

The reality is, even Hearthstone giants are susceptible to the same human error as the rest of us. In some ways, these experts more disadvantaged when it comes to accurate card predictions.

The Expert Problem

There is certainly a lot to be gained from the insight of experts. However, the predictions of experts aren’t always more accurate than those of novices.

The problem with experts is that they do not know what they do not know.
― Nassim Nicholas Taleb, The Black Swan: The Impact of the Highly Improbable

Quite frankly, despite their wealth of experience with the game, Hearthstone experts are often subject to overconfidence in their predictions. In some situations, as pointed out in Nassim Nicholas Taleb’s ground-breaking book The Black Swan, this can lead to expert predictions being (counterintuitively) less accurate than those of a novice.

In a frequently cited study by Philip Tetlock, a field of experts (PhDs) and novices (undergraduates) were tasked with predicting the likelihood of political events occurring in the near future. Not only did the experts perform no better in their forecasts, but those who were more well-regarded actually fared worse. [Author’s Note: One thing these experts were better at, however, was rationalizing their inaccuracy.]

This study showcases individuals’ (especially experts’) unwillingness to embrace uncertainty. In reality, it’s often impossible, even for the most knowledgeable among us, to accurately forecast how a single card will interact with other cards in the set and the metagame as a whole.

Authority Bias

Generally, we tend to listen more closely when an expert makes a claim. As a result, the claims of these authority figures are taken far more seriously than those of an ordinary person. The problem is that expertise doesn’t always provide more insight into a situation.

For example, playing Hearthstone optimally and evaluating cards, while seemingly inclusive, are largely independent skillsets. Even still, the card evaluations pro players provide carry more weight than those of the average Redditor (or even members of the Hearthstone Development Team).

Worse yet, even merely perceived expertise is enough to skew our response to a claim. I’m not doubting the competence of anyone specifically, but access to a webcam and a YouTube channel does not make someone an expert in game balance (no matter how many Subscribers he or she has). [Author’s Note: Yes, I recognize the irony in this statement given that I’m little more than a guy with website and a keyboard.]

The simple fact is, when a person in a position of authority makes a claim, the community is likely to repeat it, regardless of its validity. What results is a self-perpetuating belief that, simply because of the source, frequently goes unchallenged.

“I Don’t Know” is Unacceptable

Too frequently, intellectual humility is looked upon as a lack of knowledge. As such, Hearthstone experts don’t have the luxury of saying “I don’t know” in response to a card’s potential. In fact, it’s likely that any uncertainty would more damaging to their authority than being confidently incorrect in their card evaluations. Instead, pro players (perhaps sometimes unwillingly) must brazenly predict a card’s strength before even getting an opportunity to try it in game.

Decision Fatigue

Perhaps most of all, Decision Fatigue can set in quickly when pros are making their way through ratings for more than a hundred cards in an expansion. Not only does the large sample size increase the likelihood of being off the mark on a card or two, each individual Minion, Spell, and Weapon represents a choice being made.

Over time, making a long series of decisions (difficult or not) incurs mental fatigue in humans. As this fatigue sets in, judgment quickly begins to wane. Along with it, the quality of decisions starts to wane. This effect can be seen in the likelihood of favorable judicial rulings diminishing later in the day and increased odds in prescribed antibiotics over the course of a day.

I’m not here to compare the gravity of a court decision to a Hearthstone set review but one could expect that players attempting to evaluate every card in an expansion are likely to subject themselves to Decision Fatigue. Casual players are unlikely to attempt such an endeavor, but for professionals and streamers, this activity is commonplace.

It’s reasonable then, that a Neutral minion organized at the bottom of many Kobolds and Catacombs set lists would be looked upon with less than fresh eyes. By the time many experts reached Corridor Creeper, they may have already exhausted a fair amount of their mental capacity.

[Author’s Note: It was with this concept in mind that, in my own predictions, I chose a small subset of cards I rated highly, rather than an exhaustive set review.]

Looking Forward

This isn’t to say that pre-release card reviews aren’t valuable. Hearing what top-tier players have to say about a card is certainly interesting. Even community-driven ratings, while perhaps lacking some of the expertise of professional opinion, can help drive early theorycrafting.

Likewise, it’s impossible to evaluate certain cards in isolation. Obviously, those with universally powerful effects like Call to Arms and Kobold Librarian are going to find their way into decks. The potency of some cards, Corridor Creeper included, is a bit more subtle. These situationally powerful cards rely heavily on in-game playtesting to uncover their true potential. In a metagame less reliant on minion combat, we could all still be collectively overlooking Corridor Creeper.

What we need to avoid is taking these expansion predictions too seriously. The sheer number of cards printed in each expansion makes it impossible to accurately assess every card in the set. As consumers of this pre-release content, we must take these claims with a grain of salt. Moreso, we must be patient with our judgments (as well as crafting and disenchanting decisions that follow) to avoid rejecting powerful cards before new expansions are even available.

Creeping Determinism

Finally, for the sake of future expansion predictions, it’s important to avoid falling victim to the Hindsight Bias. After the fact, it’s easy to say “How could anyone miss that?” or “I knew it all along!” with regard to Corridor Creeper’s potency.

In reality, we tend to overestimate the predictability of events after they have already happened. We’re even more subject to Hindsight Bias when an event, in this case, the card’s effectiveness, is as extreme as it is. Yes, it’s clear now the card is completely broken. Few people, however, rated this as a meta breaker before seeing Team LUL dominate with it in every deck.

In order to protect our fragile egos, we, as humans, even have a tendency to distort our memories in order to validate ourselves. You’re welcome to claim that you’d been singing the praises of Corridor Creeper since the day it was revealed. I’ll even take your word for it. Just be sure you’re being honest with yourself about the validity of your predictions before making the same mistakes when previewing cards from the next Hearthstone expansion.

Game Better.

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