Mar 3, 2015

It's The Economy, Stupid: Variety In The Binding Of Isaac And Other Roguelites

I hate this boss so much

I enjoy most genres, but roguelites/roguelike-likes are a particular favorite of mine. I'm drawn in by multiple qualities: the real choices and consequences of permadeath, the focus on solid gameplay instead of narrative or visuals, the tendency for multiple short playthroughs keeping the experience tight. And the way these games make use of procedural content to offer a huge variety of scenarios, letting me fully explore a set of mechanics. And in the variety department, no other game in the genre has been able to top the sheer replayability of the Binding of Isaac (the first game or Rebirth). I often wonder why that is. When other roguelite games have tried to use Isaac's formula, or some choice bits of it, none of them really came close to the same potential for different playthroughs. They appear to just copy some shallow elements of BoI's gameplay, seemingly without understanding their purpose in the overall system.

So what is this system, exactly? What makes each playthrough in Isaac so different from the last?
Aside from procedural level generation, the item system is the first thing that comes to mind: your charater progresses by collecting items which change his stats and even alter the main attack's shape and the pattern of use. And each playthrough generates a different set of items. The item system is certainly one part of it, and the sheer size of the item pool to pull from truly varies up each playthrough. Not to mention the potential for synergies between items expanding the probability space even further.

Other roguelite games have tried to adopt a similar progression system: Ascendant, Heavy Bullets, Nuclear Throne, Paranautical Activity, Risk of Rain, Ziggurat, Tower of Guns... these are just the ones I can recall, I'm sure there's plenty of other examples. Sometimes their items just don't change enough, sometimes each item is just a "+15% fire damage" style powerup that creates a linear increase in strength over time, without causing a notable Difference in Kind, or without interesting tradeoffs and synergies to change things up on different playthroughs.

But there's something else in the Isaac formula, something which also interacts with the item progression to increase the amount of potential outcomes even further. Something less obvious, which many of the other devs seem to have failed to fully grasp. It is what I like to call Isaac's Economy.

In Isaac you have six resources: money, keys, bombs, heart containers, red hearts, and blue/black hearts. You could mix in some extra ones, like Sin or item charges, but those six are the main ones. Most other developers copying those seem to view them as a mere tool of linear progression: you slowly gain more money to buy more items from the shop, thus becoming more powerful and so on. Then those devs copy one or two resources: money and bombs (Paranautical Activity), or money, keys and blue hearts (Ascendant) or sometimes only money (Tower of Guns), and make it something you slowly accumulate to get an increase in power every X coins, even letting you choose one of the options in the shop. And it's all nice and dandy, everyone likes progression, especially when there's choice involved. But Isaac's economy provides much more than that.

All of these resources let you gain items (and thus progression) at different stages in the game, and in different ways. Bombs let you break into secret rooms or get things behind rocks. Keys are needed to get into the item rooms and stores. Coins let you buy items from the shop, gamble and get items from beggars. Heart containers and blue hearts can be traded in for particularly powerful items. Even red hearts can be gambled for items at the demon beggar, arena or the spiked door room. But this is still the same kind of linear power increase, only there's six of them instead of one or two. Here's what makes the system interesting:
1. Each resource type gives you access to a different pool of items. Item rooms can contain anything, Satan mostly offers rare and powerful items, beggars tend to give up food and so on.

2. The item opportunities show up at different points in the game for different resources. Shops and item rooms only generate on the first 6 floors, arcades can also show up in the Womb, secret rooms appear on all floors etcetera. Thus, you end up getting items at different points of each playthrough and doing different things to get them each time because of the next point:

3. Procedural generation of drops gives you a different set of resources each playthrough. Usually (but not always!) there's one or two resources you get tons of, and you end up short of everything else. So in playthrough A you get loads of money and keys, so you make your character build from going to item rooms, gambling and buying out stores, passing up all other opportunities. Then, playthrough B mostly gives you bombs and hearts, so you ignore all the stores and search for secret rooms instead. You also go into every arena and spiky door room you can find. On playthrough C you might only get money, so you gamble whenever you can. All of this changes things up: the way you see and play through floors, the pace, the timing of your item gets. You're not just picking up tons of coins to buy things in the shop every single playthrough, you do different things to gain access to different items. And you also plan and make lots of strategic choice due to point four:

4. Every resource can be exchanged for every other resource. And, just like with items, exchange opportunities show up at different stages of the game. You trade hearts for money, keys or bombs using the blood machine, arenas or spike rooms. You can trade keys for other resource types by opening the shop, opening chests and lock tiles. Bombs clear the way to other things, cards, pills and active items can exchange various resource types, either at a set rate or based on chance... And this also ties back into the item system, allowing for not only character stat oriented items but also economy-based items which can affect your resources in various ways.

As a result of all that, there's a lot of divergence involved in each run you do, and a lot of choice and planning. In a game that just uses money to give you items in shops, the choice and variation provided by economy looks (roughly) as simple this:

Not very interesting
In contrast, here's how economy resources branch out the Binding of Isaac:

I forgot PowerPoint is not a real diagram tool
This is very rough, and vastly incomplete, but you get the point. Just from that, without even taking into account gaining multiple resources (coins and bombs, hearts and keys...), stage variation or builds and potential item synergies between item groups, you get this much variation between each playthrough. This is not immediately obvious, but vastly important to Isaac's gameplay. I would argue that even the combat takes a backseat to planning out and navigating this. And yet, despite picking up superficial bits and pieces, like a cargo cult seeing the outer representation but not comprehending the real system the competitor games pretty much always seem to go for that first option.

Now, to be fair, it's possible that they might choose so deliberately, rather than due to lack of understanding. Systems like the money->shop progression existed long before Isaac, in the proper roguelike games, so maybe these rogue-lites aren't ripping Isaac off but merely following genre traditions.

It is also possible that the devs of these other games simply wanted to maintain a focus on the action and combat, rather than playthrough variation based on resource management: Isaac may blow everything else out of the water in terms of variability, but the fighting, which is a core part of the experience, isn't really as strong and fleshed-out as in many of it's competitors, shot and stat changes nonwithstanding. Fighting in the early stages is usually fairly simplistic, and the final stages seem to rely less on quick dodging and more on having assembled a build with enough power to outpace the spikes in the difficulty curve.

One could argue that the main gameplay focus of all games in the roguelite genre tends to fall somewhere on the spectrum between Luck-based Resource Management where a lack of skill in shooting and dodging doesn't matter as long as you can get items to put together the right build, and Skill-based Fighting where it's the shooting and dodging that decides if you win or lose, and managing items and character powers will only marginally improve your odds. Maybe Isaac is in the former camp, while the other examples are mostly in the latter. And for all the differences in ways of getting items, Isaac's fighting is still mostly about kiting and spamming damage spongy enemies with piddly little bullets.

Still though, despite combat variety and procedural generation, these other games have started to blur together for me after only a dozen playthroughs. And Isaac must have lasted more than a hundred, and I still come back to it from time to time, knowing it'll be a new and unexpected experience. I don't think such a complex resource economy must necessarily go against a strong combat focus, so I wish more roguelites adopted it to boost their replayability, and it always feels like a waste of potential when they don't.

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