In The Beginning

The Binding of Isaac was a little rogue-lite title created by Edmund McMillen of Super Meat Boy fame. I consider it one of the greatest self-contained works of art of PC gaming. Everything in this game: the art, the music, but especially the mechanics, came together to make a sublime experience. Like many rogue-lites, the game takes the familiar Zelda top-down mechanics and transplants them into a procedurally generated, randomized dungeon. Every level of the dungeon is randomized, and every level has a boss in the end. Additionally, in the rogue-lite tradition (which was just starting out at the time), every run in the game is different, and once you die, you have to start over.

McMillan made some very interesting, if not brave, decisions when designing Isaac. Most games shy away from giving the player too many passive bonuses. Passives are difficult to control and balance, unlike active powers, which can be controlled via cooldowns, resource limits, etc. Edmund reasoned that since every game in Isaac is fairly short, it would be ok to give the player passive bonuses that stack up — in the worst case, the player would beat the dungeon. The game is designed such that you need to beat the game many times to see all the bosses and all possible endings, which means that a particular lucky run doesn’t impact the lifetime of the game, except for possibly unlocking more stuff.

The true spice of the game – the part that kept you going – was the variety of items you could get at each shop, boss room, and secret devil deal rooms. The items were drawn from a large cache, meaning that you’d rarely see the same combination multiple times. Item variety, combined with varied room layouts and enemies, ensured that the game has had an extremely long life, with Youtubers such as NorthernLion and Bisnap recording years’ worth of videos of themselves playing Isaac.

It’s The Economy

Because of the game’s design choices, Isaac was very sensitive to passive items. While active items could only be held one at a time and had a cooldown, passives built up every time you got one, transforming Isaac’s look in the process. A few passive items could make all the difference between a difficult and an easy run, and therefore item distribution needed to be carefully controlled by the game designer. Despite the fact that each run was short and had little future impact, if the player became too powerful too consistently, the game as a whole would be impacted.

In general, I found that Isaac, together with its expansion Wrath of The Lamb, had good balance, despite the fact that some items or item combinations were clearly over-powered (OP). This is because the probabilistic balance of the game followed a nice normal distribution. Strong items were more rare, and weak items were common, as a way to balance them out.

To simplify things, we can look at runs in Isaac as chunks of the economy. You have the poor (the really unlucky runs), the middle class (the decent runs, with some good items and some bad ones) and the rich (the very lucky runs, where the player is given overly strong items). Isaac did a surprisingly good job of balancing out its wealth in a way that’s similar to a real-world economy: the majority of runs were middle class, with some poor runs, and some rich runs. A few runs were the equivalent of millionaires, where luck gave you such OP items that player skill was almost unnecessary, but these were rare, just like millionaires in real life. A very good player could use his skill to substitute for a poor run’s bad luck, but an average player would lose most poor runs, win most rich runs, and both win and lose about an even proportion of the average runs. The middle class, in other words, is where the player is most engaged, where the game is most exciting, where the tension of permadeath is felt most, and where skill plays the most role. Poor runs are almost doomed by bad luck, and rich runs are carried by good luck to the detriment of skill (and are thus boring). Isaac had a thriving middle class, meaning that despite having luck play a big role, skill was still dominant. The result of this level of balance was that you usually felt that the enemies were well-designed, that the items gave you the right edge to beat them, and that death was fair and a result of your skill or lack thereof.

I should mention that there are a few caveats to Isaac’s balancing act that need to be discussed. In order to create this really good distribution of ‘wealth’, items in Isaac needed to be balanced relative to their power. Strong items could either be balanced by negative side-effects, in which case they could occur fairly frequently in the game, or they could be left OP, in which case they needed to be proportionately rare, so that they only influenced a small percentage of runs. These principles appear to have been followed for most, but not all, items.

Brimstone is one item that was tremendously overpowered, and yet was quite commonplace in the original Isaac. Brimstone replaced Isaac’s tears, which were the main weapon in the game, with a wide laser beam of blood that crossed the entire screen. With one pickup, this single item eliminated the need to buff any of Isaac’s range, strength, or tear rate, making the game trivially easy. There was some intent to balance this item by needing a charge buildup before you could fire it. The player needed to hold the attack button for a few seconds and release it to unleash the laser beam. However, since Isaac could carry over his charge from one room to another, this requirement was fairly trivial and inconsequential. A more interesting limitation would have been to prevent movement while the laser beam was warming up, but unfortunately such an extensive and game-altering nerf wasn’t chosen. In any case, while extremely cool looking, brimstone trivialized Isaac runs, almost guaranteeing a victory. Had it been extremely rare, it would have only affected a small number of runs (the millionaire club), and allowed the general balance of the game to maintain its normal distribution. Unfortunately, brimstone turned up very often in deals with the devil, to the point that many players including myself had to refuse to take it with the full knowledge that we were handicapping ourselves, just so we could salvage our enjoyment of the game.

Another huge balance flaw was the D6, a ‘dice’ item unlocked for the main character (Isaac). Once you unlocked the D6, it became Isaac’s starting item, meaning that it was as common as an item could be. This item could reroll any item the game gave you into another item, and could be used quite often (every 3 room battles). This meant that just about every middle class or poor run could be turned into a rich/millionaire run, completely distorting the distribution of runs in the game. Advanced players who often played with the D6 probably didn’t realize how much they were distorting the game, and may in fact have a vision of Isaac’s balance as being really lopsided, when for the most part, it was very well designed.

[EDIT: The next post, Isaac and the Small Pools, discusses a large problem I initially misdiagnosed with vanilla Isaac when writing this article, and which happens to be the game’s biggest design flaw. One may consider brimstone to be a symptom of that greater malady as discussed in that post. The view of vanilla Isaac’s design from this post is more representative of the beginning to average player’s outlook, and could be seen as overly rosy.]

The greatest limitation of Isaac was the fact that it was programmed in Flash. This precluded things like gamepad support, larger rooms and smooth performance, but it did the job.

Rebirth

Enter BoI:Rebirth — the remake of Isaac in a proper game engine by Nicalis (makers of 1001 Spikes and Cave Story). I was tremendously excited for Rebirth, preordering it with the rest of the masses of fans of the first game. Edmund promised more content and a smooth engine, and I trusted him to handle the addition of new content well, just as he did with Wrath Of The Lamb — Isaac’s first expansion. While reviews have lavished praise on Rebirth, in my opinion, the results are quite mixed.

Well Done

Let us first cover what was done well in the remake. The game is extremely smooth — really, really smooth. Running at 60fps, it performs in a way that the Flash version could only dream of. Edmund also did a great job of adding dungeon variety, improving some boss attacks, making enemies that play on the themes of previous enemies, and in general, making large chunks of the game more varied and interesting. In addition, many passive items were made to synergize with each other. More on this later.

Another thing that is great to have in Rebirth is a save feature. At this point, Rebirth is a fairly long-ish game, and not being able to save in vanilla Isaac made me stop playing it — I just didn’t have a long enough chunk of time to dedicate to a full run. So I’m very glad that the ability to pick up your run and continue it is there.

Rebirth also fixed vanilla Isaac’s glaring balance flaws: the D6 has been nerfed and can be used far less often, and Brimstone is now rare due to a bigger variety of items in the devil deal item pool. This should have made Rebirth just about a perfectly balance game, but alas, it was not to be (at least not as of this writing).

Cracks in the Wall

So where do I feel Rebirth failed? Well, I feel like the balance, that was so well crafted in the previous games, is now basically broken. My first experiences with Rebirth was one that many veterans of the old game seem to have had: boot it up, play, and lose somewhere in the first couple of levels. ‘Awesome!’, I thought to myself, ‘old, cruel Isaac is back, and it’s better than ever!’. Playing another run, I hit on a cool new item. ‘Wow — that’s really cool and powerful. And it changes its behavior based on another item!’. I quickly proceeded to demolish Mom, the first big boss of the game, with almost no effort on my part. I was surprised, since this feat took me several months in the first game. Clearly, I thought to myself, this was one of Rebirth’s millionaire runs, and I just got lucky.

The problem was that most runs after that were similar to one of these first two experiences. Either I got a really bad run and died to a stupid mistake early on, or I got carried through by the huge variety of what seemed like OP items the game now had. I kept experiencing a few poor runs and many rich/millionaire runs, but almost no middle-class runs. Where was the run that gave me something good, but then screwed me over, and then gave me something else good, all the while challenging me with difficult bosses? Was I just so good at the game now that it couldn’t challenge me? I went back to vanilla Isaac to see if that was the case. Nope. Even after I got some great OP items, vanilla Isaac remained challenging. It didn’t allow me to get more than the rare rich run (I made sure not to use the D6, as mentioned above). So what is the problem?

If we compare Rebirth to Vanilla Isaac, we’ll see that the middle class is missing. Rich runs are very common, poor runs that flop occur once in a while, but middle class runs are almost nowhere to be found. Something in the game is causing middle class runs to turn into rich or millionaire runs. Another way to phrase it is that in Rebirth, skill is quickly eliminated from the game by luck — either bad or good. The result is that most runs by experienced players (who know the mechanics and enemy patterns) end in trivial, millionaire-style victories.

I have to add that I have never seen a rogue-lite title consumed as fast as Rebirth. The day after the release, people were quickly advancing from one achievement to the next. Players who never played the game before were beating mom, and then the heart (the first 2 big bosses). The game is now closer to a roll of the dice, with the result being either a sure loss (poor run) or victory (rich run). In fact, I wouldn’t even call the current version of Rebirth a rogue-lite. It’s closer to being a synergy-exploration adventure.

Unfortunately, I had to do what I hate doing, which is dive into some of the internals of the game to try and figure out the problem. I hate taking apart games like Isaac, because I love the sense of mystery that they engender. I never unlocked every achievement obsessively in vanilla Isaac — it’s just not how I play. I want to feel like there’s this great unknown black box that’s generating these wonderful, exciting experiences for me. With vanilla and WoTL, I mostly learned to trust Edmund’s judgement. With Rebirth, as I experienced, something somewhere was messed up, and I wanted to find out what it was.

Having gone further into the internals of the game, I think I figured out what the main problems are:

Too many OP items that aren’t rare enough. Remember that in order to preserve the economy of runs, items that are strong need either a countering disadvantage or high enough rarity. It turns out that all items in Isaac are equally rare, with some specific exceptions that don’t cover nearly enough of the strong items. This is a huge problem gameplay-wise, since it means that OP items’ rarity is only determined by the total number of items in the item pool. With enough strong items *in* the pool, you’ll constantly get strong items drawn *out* of the pool.

OP synergies. One complaint in Isaac was that many items that you expected to be stronger together didn’t do anything, because it wasn’t programmed in. Rebirth addresses this by adding many synergies for items. The classic synergy example is Brimstone and Tammy’s Head, the latter being an active item that normally spat out your tears in a star shape, and which could recharge after every fight. In Rebirth, Tammy’s Head combined with brimstone spits out streams of brimstone in every direction, completely covering and destroying everything onscreen. The effect is extremely cool the first time you see it, but is also extremely unbalanced. Virtually nothing can survive the onslaught of this combo, and it can be performed screen after screen.

While this wouldn’t be so bad if the aforementioned items were extremely rare, in reality, they aren’t as rare as you might think. Remember, this is only a 2 item combination — it’s not a 5 item combination, which would be legitimately rare (the probability of each item multiplied together). Also, many other OP synergies of only 2 items exist, filling up the item probability space. It’s just too easy to get a rich run due to picking up one or two powerful items, or even middling items that combine powerfully. Hence the death of the middle class.

One may also ask, why (other than the ‘cool’ factor) do we need a synergy that includes Brimstone, which is already an OP item? If you have Brimstone, you can probably beat the game as it is. If you have Brimstone and Tammy’s Head, the game is essentially over instantly, and the game should wave a little white flag on the spot.

Too many feedback loops, or in other words: the rich get richer. Vanilla Isaac always had feedback loops that rewarded rich runs. For example, devil deal rooms were much more likely to appear if you took no red-heart damage. In theory, this is built to reward skillful players. But it also rewards OP players who can buff their HP with spirit hearts, the damage of which causes no devil deal penalty. This is a feedback loop: it makes OP players become even more OP, because now they have access to devil room deals, which almost always offer strong items or resources. Each such ‘rich get richer’ scheme works to skew the economy of runs, turning middle class runs into rich/millionaire runs. Rebirth seems to increase the occurrence of devil rooms, which in turn amplifies this feedback loop even further. Additionally, Rebirth added a new way to automatically access the devil rooms: the Goat’s Head item, which is common since it exists in several item pools, gives you access to every devil room deal.

Mushrooms and Skulls: Another example of a completely new feedback loop is the destructible mushrooms and skulls that exist in some specific levels. Vanilla Isaac had rare tinted rocks in the first few levels that when blown up, give the player spirit hearts and possibly bombs. This was a feedback loop of sorts: strong players who had bombs (or no use for them) could blow up the tinted rocks, getting more resources for themselves. However, it wasn’t so bad, mostly because the first few levels didn’t give you enough time to build up a wealth advantage. Runs were mostly differentiated in the later stages.

Rebirth takes this to a whole new level, adding levels packed full of destructible mushrooms, which give you pills and even stat-boosting items, and skulls, which give you cards. Both pills and cards can be used to boost your stats and gain resources, making you ever more powerful. However, these resources are only available to those who either have the power to smash destructibles (a new power introduced in Rebirth) or for players with either many bombs or no use for the bombs they have (ie. the rich). Once again, the rich get richer.

The worst manifestation of mushrooms and skulls happens when they cluster together in small clumps. In these cases, the player can place one bomb in the middle, rolling up to 4 drops at the same time, and showering himself with resources. So many more resources are available in the middle layers of Isaac that you actually get sick of cards and pills, while in vanilla Isaac they were a rare, cherished commodity.

Black Hearts. A new addition to the mix of HP types in Rebirth is the black heart. This heart, much like the spirit heart, can be added past your regular red HP pool and counts just like a spirit heart for all practical purposes. It is, however, much stronger than a regular spirit heart, in that destroying one of these hearts hands out massive damage to anything on-screen. This is a huge change of mechanics from vanilla Isaac, and is probably one of the big differences making Rebirth easier. Normally, a room where you take damage is probably one that exploits some weakness your character has, and will likely lead to taking more damage. In Rebirth, if you happen to have a black heart, taking damage will likely wipe out everything in the room, no matter how far away from you, thus eliminating the threat. This mechanic itself is OP — a better, more localized effect could easily have been thought up. But it also tends to favor the already powerful runs. Such runs often tend to be accompanied by large collections of black hearts. When finally encountering a challenging room, the threat is quickly put down due to a black heart.

Fewer Crappy Items. Playing vanilla Isaac, I realized that the game often gave you crappy items — ones that contributed little to your power or that you just wanted to skip. Rebirth tries to make more items useful, and in doing so, perhaps gives you too many useful items and not enough crappy ones. The best crappy items are those that are situational. For example, Pageant Boy gives you a whole bunch of coins, which is not particularly useful to advance your character, unless you’re really short on cash. Poop, on the other hand, is literally a crappy item, generating a poop when you use it. Both kinds of items are useful in diluting the item pool.

Old Monsters, New Tricks. Rebirth uses mostly the same monsters from vanilla. These monsters were great: they were grotesque yet cute, they moved in different patterns, jumped around, left bloody, poison trails on the ground, etc. But they weren’t built to handle the level of player power that results from so many extremely rich runs. Even the new monsters added in Rebirth aren’t really equipped to handle the level of OP-ness that constantly gets handed to the player. A common experience in Rebirth is to proceed from one screen to the next, demolishing every poor, hopeless critter onscreen with one fancy bullet pattern or another.

What To Do?

So now that we’ve seen the balance problems in Rebirth, what can be done to fix them? I think a few things can be done.

The drop rates of mushrooms and skulls can be lowered so they’re not as powerful. Perhaps more dangerous consequences can be introduced to blowing up the wrong mushroom/skull, so there’s some risk involved (the current consequences are too minimal).

The effects of black hearts can be toned down. They could do less damage, or at least do localized damage around Isaac.

Mushrooms and skull clusters can be reduced, so it’s not so easy to hit so many of them at once. This reduces the incentive to pop them, since the chances of rewards are much smaller.

Either more items need to be made Special, or a proper rarity system needs to be implemented.

We need more crappy items in the item pools. For example, the chest item pool easily turns you into Guppy (essentially a god mode consisting of 3 Guppy items) because it has too few drops available.

OP synergies need to be balanced as well, particularly if they’re not rare. For example, Tammy’s Head + Brimstone could gain a longer cooldown.

I think these solutions could go a long way towards restoring the probabilistic balance of Rebirth and its missing middle class. Currently Rebirth often feels more like a monster punching bag simulator rather than a tense game, and I hope that can be corrected.