The Binding of Isaac Gameplay explained

So, I've obviously been seriously neglecting this dev blog due to crunch time with The Binding of Isaac, but things are currently slowing down due to the game being basically finished minus some more testing and polish so i thought it would be a great time to do my 1st in depth blog post about the design of Isaac.

For the past month we have been heavily testing Isaac with other devs, the response is extremely positive and the majority of testers are fully hooked, but there is one core issue.

The 1st time people play they don't understand that the game was meant to be played multiple times with different results.

I've tried to push the title "Roguelike" around a lot to get across how the game plays, but I'm now realizing that a majority have no clue what that means, they see something that looks like a zelda shooter and right away assume it's going to be a linear experience and then become frustrated by their 1st death when they respawn back at start.

So here is my attempt at explaining the game :) I think I'll call it...

Randomly Generated Content! it's good for you!

The goal with Isaac was simple, I wanted to design a game that would feel totally fresh and new every time you play it. Now on paper this might seem very hard to do, but by pulling from the roguelike formula I was able to do this pretty easily.

On the surface the first thing most people will notice after playing once and dying is that the maps are generated randomly.

Every map consists of 4 core rooms, and between 5-20 non-core rooms.

The 4 core rooms are:

Treasure Room: where you will always find an item

Boss Room: where you fight the boss end exit the map

Shop: where you can buy items

Secret Room: its a secret!

The 4 core rooms will ALWAYS appear in a map, they are the foundation of the games "leveling" system and should be looked at as the goals of each level. Even though these rooms always appear, their contents, enemies, look, design and any "surprises" within them are randomly picked from a slew of alternates.

The non-core rooms are randomly selected from a pre-designed group of 1000+ rooms that are arranged by difficulty and chapter. the majority of these rooms consist of small arena battles that make the bulk of the game play, but they are also peppered with bonus rooms with mini puzzles, prizes, traps and a few surprises here and there.

Aside from these rooms there are also a set of context sensitive rooms:

The Arcade: A room filled with mini games that cost coins (only appears when you have enough money)

The Challenge Room: Fight off waves of enemies for a prize. (only appears when you play well)

Mini boss room: a mini boss appears!

Mystery Room1: it's a secret!

Mystery Room2: it's a secret!

These uncommon rooms are meant to spice up game play and add small alternate goals and or extra risk/reward aspects to the game. as per usual the contents of each of these rooms is always different.

On the surface this is basically the foundation of the games design, but if we go another layer deeper we can see that the contents within the randomly generated core content also have random elements inside of them.

Now, we know that the rooms are chosen randomly from a very large set of rooms I designed, but the contents within each of those rooms also have random elements.

Enemies:

There are well over 50 enemies in Isaac, but each of these enemies have minor random elements:

For example we have this guy, the Mulligan.

Most of the time he looks like the 1st guy, runs away from you if he sees you, has a small % chance of blowing up and shooting bullets out and spawns 2-4 randomly chosen flies when he is killed.

But there is also a smaller % chance he will appear as the 2nd guy, the Mulligoon.

Mulligoons act the same as their brothers accept they always explode into a spray of bullets when they die and also leave a "troll bomb" behind that blows up.

On top of these there is an even smaller % chance that a Mulligan will appear as a "Special" Mulligan and possibly look like the 3rd guy.

Special enemies will be randomly colored, slightly larger then their brothers, do more damage and have more health.

Special enemies will also drop "pickups" when they are killed as an extra reward for the risk of fighting a stronger enemy.

Pickups:

Whenever you clear a room, kill a special enemy or open a chest there is a good % chance pickup items will be spawned.

Core pickup items consist of:

Pennies: you buy items, play games and donate these to hobos.

Hearts: you fill up your life with these

Bombs: you blow up rocks, doors, walls and enemies with these

Keys: you unlock shops, treasure rooms, locked chests and other special things with these.

Less common are the one use pickup items:

Tarot Cards: randomly picked from the 18 cards that exist in the game. each card has a different effect.

Pills: randomly picked from around 12 different effects, both negative and positive. every new game changes what color pill has what effect(much like scrolls and potions in roguelikes.

On top of these, there is also a small % chance that the core pickups will become these:

Nickle: 5 pennies!

Half Heart: :(

Soul Heart: acts as armor

Double bomb: 2 bombs

Troll Bomb: :(

there is also an even smaller % chance that rooms, enemies and the like will generate chests, there are 2 types of chests

Basic chest: Generates 2-5 pickup items, can also appear in mini puzzle rooms

Locked Golden chest: Generates 2-8 pickup items, can also generate "special items"

Special items:

Special items are the core of the games "leveling system". Similar to Zeldas leveling system (if you can call it that) Isaacs growth focuses on finding items that stack together, raise your stats, change how you play and how your character appears in game.

There are over 110 special items in the game that fit into these categories.

Usable items:

these items all have different effects when you use them and recharge by completing rooms. items have different charge rates depending on the power of the item, you can only hold one Usable item at a time.

Weapon items:

these items change your shots adding properties like homing, poison, knock back, boomarang etc. They might also totally change your attack to something very different.

Stat padding items:

these items raise your range, damage, rate of fire, speed and HP (adding container hearts)

Passive items:

these wild card items will effect many aspects of gameplay without having to do anything, they range from gaining the ability to see through walls, to the ability to fly.

Familiars:

these items act as "Options" (like in Gradius), following the player+shooting, blocking, finding/generating pickups or just running around killing stuff.

The majority of special items are found in treasure rooms but, less common items are also found exclusively in other rooms:

-The Shop has a set of exclusive shop items that usually aid ease of level traversing

-The secret room has a set of more odd and rare items inside it

-The Boss room has a set of stat padding items to make sure your character's stats always get raised.

There are also small sets of very rare items exclusive to other "things" but i wont spoil them.

and finally...

Bosses:

As mentioned before, every map in the game will feature a boss room where you face off against one of 20+ bosses, killing the boss will get you a stat padding item and open the trap door to the next level.

Like everything else in the game, bosses are also randomly chosen and have random elements within them.

Every time a map is generated, it picks a boss from a set of 4-5 bosses for that chapter set. each chapter consists of 2 levels, if it's the 2nd level of the chapter the boss that is picked gets slightly buffed HP wise to balance difficulty.

The bosses level is randomly chosen from 8 different arena layouts, sometimes appearing with "helpers" or small mobs. Like enemies, Bosses can also appear as alternate special bosses with modded stats, attacks and visual changes always keeping you on your toes.

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All in all the stacking of these elements along with extra "special happenings" and other undescribed extras makes this formula of random generation create a game that is so different each time you play it that the penalty of having to start over from scratch really becomes a reward, because every time you start a new game the adventure feels totally fresh and mysterious.

There is another huge element to all of this that rewards players even more, but ill hold off on explaining that till the next post.

If you have any questions feel free to ask them in the comments.

The Binding of Isaac will be launching on Steam (Pc/Mac) in the next 2 weeks.

-Edmund