Roguelikes have always been a tad frustrating for new players, being as unforgiving and generally hard as they are. Forcing your players to start over from nothing almost seems counter-intuitive if your interest as a developer is to keep the player in their seat playing your game. Conversely, they actually seem to be a clever solution to the problem of replayability. Generally when you complete a linear game, that's it. You’ve beaten the game, and there's nothing left to see. Aside from maybe some side quests or collectables, the game has lost its value to the player. The dragon is slain, or the princess is rescued, and the game goes back on the shelf and becomes a fond memory. However, roguelikes generally have this wonderful quality of being procedurally generated.
This means that every time the player chooses to go round again with your staunch, unforgiving, rouge-slaying dungeon, the experience will be entirely unique. It’s as if the player is beginning on a new quest, playing through a new dungeon entirely. And the production of the dungeons isn't the only place where randomness plays a role in the success of these types of games. The Binding of Isaac games are a perfect example of the role that randomness can play in improving a title’s replayability. The Binding of Isaac: Rebirth has a total of 341 distinct items in the base game, most of which change gameplay entirely, some even randomizing stats or other game elements. That’s a lot of RNG.
Chance as a balancing mechanism
So in order to understand why a game developer would rely on chance for their game to have any semblance of replayability, we first have to understand some basic ideas in game balance. Game balance is an odd topic when talking about single player games, because generally when it gets brought up, it’s referring to the perceived effectiveness of a mechanic in a player vs. player setting. However, this is a bit of a misconception: even in a single player game there is a fine balance between unplayably hard, and laughably easy. If a player finds themselves losing over and over, they may get up and leave. Conversely, if it’s too easy, they may get bored of the title. So as a developer it’s important to keep new players winning small battles and to keep more experienced players on their toes.
The Binding of Isaac does this in a lot of ways, but one clever example revolves around an item in the game called ‘The Bible’. This item is in the game almost solely for the benefit of new players. The Binding of Isaac has several tiers of final bosses, but the first two tiers, Mom and Mom’s heart, are killed instantly with a single use of this item. All subsequent bosses are unaffected, except Satan, who will instantly kill Isaac upon use of this item. To a new player, the discovery of this mechanic is monumental. The skill level required to beat Mom or Mom’s heart without some cheesy mechanic on your side is basically unreachable until you’ve put more than a few hours into the game. This item lets you do it instantly. To a veteran player, this item is garbage. Sure, it gets you past Mom and Mom’s heart, but if you’ve sunk more than a few hours into the game, those bosses generally aren't the ones you’re worried about, and there are slightly better items to be carrying around that require a little more skill to use effectively.
This allows for newer players to be immediately capable of beating these bosses, with lower levels of skill. The outcome of beating Mom and Mom’s heart is the same whether or not you cheesed them with the bible, and both outcomes produce the same amount of satisfaction with different skill input. Newer players get the satisfaction of winning and keep coming back to play the game over and over. They then slowly pick up skills and strategies with other items. As they progress further, the items that may have been perceived as garbage before, when used with a bit more skill, end up being just slightly more powerful than previous items. This keeps experienced players trying new items and strategies to further their potential power output with their higher skill input.
Why Isaac works
The kicker is that The Bible is random and only a single entity in a huge pool of random items. This means that as a new player, there’s only a small chance you’ll get lucky and find The Bible; that chance is what would drive you to keep playing. You might possibly find a good set of items and blaze through the game with ease, or you might get mediocre items and have to scrape by and learn a few things. But the chance of winning is still there as a new player, and as an old player, there is the satisfying thrill of working with what the game gave you to come up with a winning strategy.
But of course, RNG isn’t always bibles and matricide. Bad luck generally plagues games who rely on RNG, discouraging players who lose frequently simply because the odds were stacked against them. If a player constantly gets poor items, it might be discouraging and force the player to give up, simply because the game keeps giving them bad numbers. As a developer, it’s important to provide the player with mechanics that give them control, even if it’s just perceived control over the random elements.
The Binding of Isaac of course has a few elements for this purpose. The most obvious one is the item called the d6. The character Isaac, after beating the game once, starts with this item and it allows the player to re-roll any items found by the player. This pushes the odds for the player to find the item they’re looking for in their favor. Should the player not like the first item provided to them, they have a second chance to find something good. This is clever because it doesn’t entirely eliminate the threat of bad RNG, but it mitigates it. It gives the player a sense of control over which items they take and which items they re-roll for better items. It’s still random and thrilling, but with a lower chance of providing the player with dull, useless items.