The Binding of Isaac and Difficulty Curves

The Binding of Isaac is one of the best games that I’ve played in years. It takes some good things from roguelikes, some good things from action role-playing games, and some good things from twin-stick shooters, throws them in a blender, and delivers an absolutely amazing experience from start to finish. With over 200 hours into it (and all the achievements), I think it’s safe to say that I liked the game. I’m not going to go into detail about the game itself, as by this point plenty of other people have done that.

About a month and a half ago, an expansion was released. Wrath of the Lamb details were leaked here and there, and I was getting more and more excited to see what would be added and expanded. There were some really interesting mechanics that were added to encourage riskier play (some great commentary from Edmund McMillen here), but unfortunately it came at the cost of the beauty of the original’s structure and difficulty curve. The guys at Extra Credits did a great piece on power creep recently, so I’ll simply direct you to them and mention that this is almost a textbook example of power creep destroying a carefully balanced system.

Difficulty curves like the one below are standard, and tend to be ideal in most cases. The challenge grows, then a bit of relaxation, then it grows again, and continually brings the player through the game advancing their skills while continuing to challenge them. This, in a nutshell, was the original Binding of Isaac. Sometimes a specific item early on would make the peaks in the curve much lower, but the game always followed the general progression.

Ideal Difficulty Curve
Power creep, as mentioned, was a problem with Wrath of the Lamb. While a large number of items weren’t necessarily stronger but encouraged different gameplay, a few were game-breakingly powerful, either individually or in pairs. I can only assume that this was known, because the expansion boosted the difficulty quite a few notches — and here’s the issue — randomly and unevenly.

Now, one of the best things about roguelikes that was stolen by Binding of Isaac is random level generation. This allows a game to always feel fresh and new, no matter how often you play it. They did a great job of having designed rooms organized in a random fashion deliver a different experience from game to game. Each level you progressed would be slightly larger and more difficult on average, but every now and then you’d get a level that was a tiny bit harder than the one to follow it which kept the player on their toes.

Wrath of the Lamb, however, throws some interesting new twists into the random generation formula. Two are interesting and valid twists, but the third wrecks the curve, especially when combined with either of the first two. First, there is “Curse of the Lost” which results in the level you’re on being generated as if it were one level further. This is a valid tweak, and can be compared to things like out-of-depths monsters in other roguelikes. The second is “Curse of the Labyrinth,” which combines your current level and the one below it into one massive level. This is also interesting, as it changes the style of play due to the potential for more exploration or a quick run through two bosses, depending on the player and setup. However, that brings us to the third.

Each level has an easy or a hard mode,  and which one a player lands in is random. These are not subtle differences either, especially at the early levels. For example, a “Curse of the Lost” hard opening level may very well be more difficult than the next three levels the player sees. This breaks the difficulty curve, and in my case, results in scumming if I received as poor first level. Even without either of the “Curse” addition, these hard-mode levels break up the smooth curve, resulting in jarring leaps from hard to easy and vice versa at random intervals. If the player had a choice upon moving to the next level, the easy vs. hard setup would be fantastic. It would allow an over-powered (or challenge-minded) player to take a harder path and roll the dice for better items, while at the same time allowing a luck-deprived player the ability to skate through a couple easier levels in hopes of gaining strength and moving on to the harder side. This option is already present at what was the original end of the game, but nowhere before. It would be trivial to add more interesting temptations to the harder path as well, since the game already has a multitude of ending possibilities and “final” bosses.

The Wrath of the Lamb expansion didn’t destroy The Binding of Isaac. It’s still a good game, even with the expansion. The problem is that the original was a damn near perfect game, and the fiddling and tweaking just upset the precarious balance that had been achieved.

Then again, Edmund’s games have sold millions of copies, whereas I’ve never even finished developing a game…

* Image stolen from an interesting post on difficulty curves and their relation to narratives.

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