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Path Length: Why no one uses Chum


Originally published at: http://stimhack.com/path-length-why-no-one-uses-chum-2/

Discuss the latest article here.


It’s not a bad method of assessing the resource battle. However in regard to Chum I think it misses a couple of things in reducing it to “Chum effectively adds two credits to path length (excluding fixed breakers)”:

  • As well as adding to path length (i.e. cost to get in), when the next ICE is unrezzed, it adds a potential cost to failing to get: three cards. Chum is most scary when the Corp is sitting on fifteen credits after rezzing it: the next ICE could be anything.
  • Even when all cards are rezzed, it boosts “porous” ICE after it (ICE that the Runner could run through taking the hit, make a trace instead of breaking, or only break some subroutines). Things like Gutenberg, Enforcer, Ichi. In that case the path length is likely to be the cost of actually breaking the Chum, rather than the 2 credits for the strength boost on the next ICE.


I always thought this was the reason no one used Chum:


Interesting article in terms of formalizing how taxing a server is. I think a lot of experienced Netrunner players do this sort of thinking already out of habit (“It will cost him X credits to get into this remote, and I have Caprice, so he won’t have enough to run twice, etc…”).

The Chum example is off to me because I feel like it’s exclusively being evaluated in the scenario of the runner already having the breakers installed. That’s fair for the purposes of showing how Chum doesn’t increase the cost of getting into a server once they have a breaker installed for the ICE after Chum, but I consider Chum to be a positional gear-check ICE. Chum is almost never, ever going to deal the net damage, because runners immediately jack out after letting Chum fire, effectively making it an ETR ICE. In order for a runner to safely run through the ICE after Chum, they have to have a decoder first to be able to safely face-check the following ICE. Then, once they know what that ICE is, they can safely let Chum fire and break the following ICE for cheaper than it would take to break Chum. At that point, Chum’s job is over, and should probably be replaced with a different ICE. The corp player should keep this in mind when they think about how to position Chum, and have a plan to replace Chum as well.

The the other thing you could do is never rez the ICE after Chum, which forces them to have to always break Chum, on the off-chance you are just waiting for them to let Chum fire so you can rez your Kitsune or Data Mine or what-have-you. In that case, Chum is sort of like a 2-cost gear check (1 to rez + 1 to install). Whether anyone would actually do this, I don’t know, but I mention it for the sake of completeness.

There is another card in D&D that reminds me a lot of Chum: TL;DR. It, too, is a 1-rez 4-str code gate that messes with the ICE that comes after it, but I feel like it does so more effectively because the way the ICE gets changed is based on that ICE itself, not a static buff like Chum. If you only TL;DR a Wall of Static, sure, you only increase the Path Length by 1. But suppose you TL;DR an Eli 1.0? That still only increases the Path Length by 2 using Corroder, but if the runner is breaking with Lady, then it’s taxing Lady counters, which could be particularly valuable, and something the runner might consider bad enough to want to break the TL;DR before continuing to run the server.

Once TL;DR comes before an ICE with 3 subs, then we’re cooking with gas. TL;DR into a Grail ICE is a fantastic way to make the server more taxing and threatening, because breaking the TL;DR and the 3 extra subs is the same cost to A Gordian Blade, or requires a datasucker for Yog.0. Net-Ready Yog can shut it down pretty hard.

Both Chum and TL;DR can also do well when considering ICE that the runner doesn’t ever want to break, anyway, or maybe even isn’t ever able to break. For example, Chum or TL;DR into a Gutenberg on R&D seems pretty brutal to me, since few runners have effective ways at breaking a 6-strength sentry, usually opting to just pay the trace, which is great news for TL;DR and Chum.

If you can create ICE situations where not breaking TL;DR or Chum causes much worse things to happen than simply costing the runner an extra credit or two on the following ICE, then they are worthwhile, IMO. But you kind of have to keep that in mind when assembling your ICE suite. You can’t just tack these onto any old ICE suite and call it a day, you have to have a real plan for how you intend to use them.


Why? If you parasite the ice behind a chum you take 3 net durring the run.

The reason you don’t play it is often because its positional and only valuable during a small window during the game.

If you’re saying that the chum gets turned off when its the innermost ice; yes, I agree.

“Path Length” isn’t really a foreign concept, though this is the most rigorous article on it so far. I’ve thought about netrunner in this manner for a very long time. And anyone who builds a taxing deck successfully probably intuitively understands these concepts, but its nice to have it formalized.

I normally consider it as “Accesses” vs “Cost to Access” and I wrote something up a long time ago on BGG. (I believe I considered Cell Portal at the time)


The analysis is interesting and relevant, however I’m slightly uncertain over how you’ve handled the caprice game and random HQ access. I would be interested to know why you don’t simply use path length for one run * the expected number of runs required to score the agenda. In the example you give of one agenda in a five card hand this would give a value of ~3.1B rather than 5B. You evaluate the Caprice game in the same way, which to me seems like an error.

Basically I believe your sequence should be p(success)* (1 + p(fail) + p(fail)^2 + p(fail)^3+ …) times by whatever the expected cost of an access is. This would give 1.71*(B+1) for the caprice game as the expected path length to the agenda.


Yeah, Chum can be an invisible ETR, often enough. I’m surprised you’re talking about it in the same way you might talk about Chimera–I don’t think it lends itself to a rush-style deck. I have been thinking about writing about the costs to install icebreakers or check out a shell game in a follow-up article. We’ll see how that goes.


This is a great article. Full stop. Awesome.

I like to think of netrunner having additive taxes, and multiplicative taxes. Adding another ice on a server increases the cost of that server solely by the cost of the ice. Using Caprice or Ash increase it multiplicatively by the # of ice in the server. Midway station grid is similar (unless your ice are high-strength). Nothing surprising, and very similar to your analysis. The interesting thing is where other effects that are a combination of both, sneak in. A server with 2 Next ice is not additively increased (as normal) when you add a 3rd. The tax is increased by closer to 2 * tax where the per-ice tax realistically taxes like an additional ice on the server (given realistic #s of ice). Grail is similar, but triggered when drawing another grail, rather than playing an ice.

Great article! Don’t let everyone side track you with the intricacies of the chum example. That’s the danger with any specific example, it is never 100% correct if you want it to be anything less than the main topic of the article.


Enjoyed the article, to me the most relevant part is when looking at the PL when combined with upgrades in the server, when building decks.

In actual game play the PL is much more variable, how many cards the runner has, what other threat have i got out they have to deal with all combine change its meaning, Either way keep it up!


This article was excellent. There are a couple of things I’ve thought about in relation to some of the ideas here. One of the big things is the ratio of cost of an ice to break cost, and what the additional trade off is with total break cost.

Eli for example, has one of the best ratios in the gams, costing 4 to break with corroder and 3 to Rez. Not a ton of other ice has such a great ratio. However, there are a couple of ice that do have larger ones. Largely popup and pup, which have “infinite” and 2 as their ratios. These are all obviously great ice that see a lot if play, but for a couple of reasons that everyone would just play 18 popups if they could.

One is that if you want to make a taxing server that is more than 1/2, you need to pay the install cost of the given ice. So the second pup has a much worse ratio of 1 (which is still good) while the third one has a ratio of 2/3. Bigger ice scales much better off of install cost (Eli goes 4/3 1 4/5, tollbooth 7/8, 7/9, 7/10). So when you want to make a really taxin server, big ice are often better because they don’t have the problem of scaling poorly off of install cost. Small ice super efficient ice are good for making a server too much of a pain to run on a lot. While big ice are good for making a server a pain to run at all.

The other thing is if you want to make a racing server out of small ice, you’re going to need a gazillion deck slots of small ice to do so. So large ice tends to be more decks lot efficient for making big racing servers as a core plan. Though most glacier decks include both so they don’t just bleed free accesses in the early game against runners built for that.


Thank you for mentioning the Twins.

This high variance upgrade can be a hilarious tool with Curtain Wall, Archer, and even Hive. And sometimes the damn smoothest bluff you can ever pull. (Rez Twins as Runner approaches Curtain Wall. They end the run in lieu of greener pastures. No Curtains in HQ.)


I once bluffed a Simone Diego as something that could have helped me protect a vanity project. Damn smooth indeed, those are the best bluffs


Remembers me of when I tried Shell corp in RP.
Its best use was “looks like caprice” ^^


Chum is semi awesome. I think people don’t use for multiple reasons (atman sucker - gordian blade made people stoping using it then the hype codegate was Inazuma).

I’m still a fan of Hunter :slight_smile:


The article is spot-on from the side of maths, and that’s a large part of Netrunner. I wonder if this could be employed to create a decent Netrunner-playing AI.

Fortunately, there’s also a lot of psychology in the game, and that’s something that is hard to capture with equations :wink:


Netrunner AI, eh? Sounds like a good idea for a thread


Great article, but…

As much as I love the math and specifically the math this game has, I strongly believe that you can’t compare cards to each other based on how they break the math in each game. There are so many scenarios that could play out differently for each of those cards.

-Experiential Data: Could bump the strength of an ice that the runner thought could break because of his datasucker tokens.
-Chum: Could be placed in front of an ICE that is super hard to break, despite the fact that it might not “end the run” or something alike. Gutenberg for example. The 3 cards loss can be so good in that case and after that, the runner will have to break chum EVERY time he goes through there if he doesn’t want to lose 3 cards. So we rezzed an ice for 1 credit and it costs the runner 3 credits to go through.
-Ash: I want to compare this so much to corporate troubleshooter. Ash is like a “better Corporate Troubleshooter” when it comes to certain cases. If you aren’t willing to just REALLY make an ice fire, then you just play Ash, since most (if not all) corps want to score Agendas in games. Having said that though, you should still not see as one being better than the other.

I am not saying the article said “this is better than this.” I’m just stating that I often see that people like to look at the math of a card and not the value it offers through other circumstances. Of course, the “better” cards have a better win ratio because they work more often and better with certain other cards.

Another example: goal of the game is to score out, so ash is definitely better in most cases than corporate troubleshooter is, since the last one needs certain combo pieces in order to work.

So in that case, you need to consider if that “out of the box” card is well worth the risk compared to other ones.


Given the subject of the article is the math of cards, talking about the circumstantial value of cards is a different topic.


I see what you mean, but the circumstantial value of cards also has math involved. So in the end of the day, it’s all the same topic.

Seeing how many times it will be worth it during a game and against what percentage of match-ups it will pay off in a tournament or so, also has value derived from numbers.

So I do believe I was no point here.


I get that there are some circumstances where cards that don’t typically shine can make a huge impact, but decks are typically built and played so that these corner cases don’t come up. For example, let’s take your Experiential Data situation: For the corp to force ED to work, they’d have to install the upgrade, taking a click, and purge viruses, and only then can the remote be considered secure. This takes two turns, giving the Runner plenty of time to counter the strategy.

A lot of readers have brought up these corner cases, and I’m glad they’ve done so! The way I see it, this article has put in words what a lot of players have intuited through many different games. This lets people hone in on places where cards that don’t have a lot of value can add to the situation. I’d contend that ED will basically never see play–the costs here scale triangularly for the Corp, but linearly for the runner–but most of the other cards I’ve mentioned are certainly salvageable.