The Binding of Isaac (2011 Original): Complete Guide

A guide to the original 2011 Flash version of The Binding of Isaac and its Wrath of the Lamb expansion: how runs work, floors and bosses, unlock goals, Hard Mode, and why most players today should jump to The Binding of Isaac: Rebirth instead.

Researched September 2026 — current as of the final Steam build of the original game plus Wrath of the Lamb (no further updates; all active development moved to Rebirth and its Repentance+ DLC). Live games change; check the linked sources if something differs.

Important: This page is about the original 2011 game (Steam app 113200), built in Adobe Flash. The actively supported version is The Binding of Isaac: Rebirth (November 2014), a full remake with far more content, native controller support, co-op and ongoing updates through its Afterbirth, Afterbirth+, Repentance and Repentance+ DLCs. If you are new, buy Rebirth. Play the original for history, achievements, or curiosity.

Quick Start

1. It is a roguelike twin-stick shooter. You move with one set of keys and shoot tears in four directions with another. Each run is randomly generated and permanent death sends you back to the start.
2. Default keys: WASD to move, arrow keys to shoot, E to place a bomb, Space to use your active item, Q to use a pill or card.
3. Explore every room on early floors. Items, pickups and shops early in a run decide whether you can survive later.
4. Always check the Treasure Room. Each floor normally has one item room; its item is usually the biggest power spike on that floor.
5. Keys, bombs and coins are currencies. Keys open locked doors and chests, bombs open secret rooms and tinted rocks, coins buy from shops.
6. Items stack. Most passive items combine, so a run can snowball into something absurd.
7. Unlocks come from achievements. Most new items, characters and chapters are unlocked by completing specific goals, so early runs feel sparse.
8. Expect Flash-era performance. The game can slow down in busy rooms and has limited controller support. That is the engine, not your PC.

Original vs Rebirth: Which to Play

Edmund McMillen has said he would not have used Flash had he known how popular Isaac would become. Rebirth exists largely because of those limits.

How a Run Works

1. Start in the Basement with the chosen character's stats and items.
2. Clear rooms by killing enemies; doors lock until the room is clear.
3. Find the boss room and beat the boss to reveal a trapdoor to the next floor. Beating the boss also drops an item.
4. Optional rooms: Treasure Room (item), Shop (buy with coins), secret rooms (bomb walls), Arcade, Challenge rooms, Sacrifice rooms and more.
5. After a boss, a Devil deal or Angel room may appear; Devil deals trade heart containers for powerful items.
6. Repeat until you win or die.

Chapter structure

The base game has 4 chapters spanning 8 levels, with Wrath of the Lamb adding alternate versions and two more optional levels.

Beating Mom's Heart is the first real "ending". Repeated completions unlock more endings and the optional chapters.

Characters

The original has seven characters, each with different speed, health and damage:

Characters beyond Isaac are unlocked by in-game goals. The Steam achievement list spells out Samson's: kill Mom while passing on two Treasure Room items in that run (leave them on their pedestals). For the others, check a wiki's unlock list for the original game (not Rebirth, whose conditions differ).

Each character then has their own completion unlocks. From the achievement list:

Full-game clears also unlock The Bag (Cain), The Cross (Maggy) and The Robo-Baby (Judas); Samson killing Mom's Heart unlocks Blood Lust.

Useful Unlock Goals

The Steam achievements double as the unlock list. Several easy-to-target ones for early runs:

Repeatedly completing the full game unlocks a chain of items (The Noose, The Nail, The Quarter, The Fetus, and so on up to "It Lives!" at 9 completions). Character-specific completions unlock character items: for example, completing Sheol with Isaac unlocks Mom's Knife, and completing the final chapter with Isaac unlocks The D20.

The game also has nine numbered Challenges; completing them unlocks items such as The Candle (Challenge 1), The Lucky Toe (Challenge 2), The Burnt Penny (Challenge 3), Guppy's Tail (Challenge 4), The Fish Head (Challenge 5), Mega Fetus (Challenge 6), Super SMB Fan (Challenge 7), The Spider Butt (Challenge 8) and The Counterfeit Coin (Challenge 9).

Hard Mode

Wrath of the Lamb adds a Hard Mode with Eternal Hearts and its own achievement set: beating Mom, Mom's Heart, the Cathedral boss and Satan on Hard, finishing with every character on Hard, and "Eternal God" for 100% plus all Hard Mode achievements. Hard Mode is the true completionist grind, and the Steam stats show only around 2% of players finishing it.

Hard Mode tips:

• Play Judas or Isaac first; ??? on Hard is notoriously difficult (the achievement text literally says "good luck").
• Take Devil deals carefully. Losing containers hurts more when enemies hit harder.
• Fully explore Chapters 1 and 2 to build up before the Depths.

Core Survival Tips

• Learn enemy tells. Most enemies have a wind-up; shoot, then sidestep.
• Use doorways. Standing near an entrance lets you retreat into the previous room to reset positioning.
• Bomb suspicious walls. Secret rooms usually sit next to several rooms; bombs also clear rocks for items.
• Don't waste keys on low-value chests when a Treasure Room or shop needs them.
• Shops are worth it if you have coins; buy health or a strong item before a boss.
• Pills are gambles. Once identified, a pill's effect is known for the rest of the run. Test unknown pills when you are healthy.
• Special ("champion") enemies are tougher but drop better loot. Kill them when safe.

Common Mistakes to Avoid

• Rushing floors. Skipping rooms means skipping items. Full clears pay off, especially early.
• Taking every Devil deal. A great item is not worth leaving yourself one hit from death before Mom.
• Playing on a controller expecting Rebirth-level support. The original's controller support is limited; keyboard is the reliable input.
• Assuming Rebirth guides apply. Many Rebirth items, floors, characters and bosses do not exist here. Use original-game resources.
• Expecting co-op. There is none in the original.

Advanced Tips

• Keep one bomb for secret rooms on each floor.
• Save your active item for boss fights or dangerous rooms, then recharge it by clearing easy ones.
• Route unlocks deliberately. Stack goals in one run: donate blood, hoard pennies and chase heart containers at the same time.
• Use Challenges to unlock items that make normal runs stronger.
• Performance fixes: close other browser/Flash-heavy apps and run at a lower window size if rooms stutter. The original is a Flash projector app on Steam and does not need a browser plugin.

FAQ

Is the original Binding of Isaac still worth playing? For history or achievements, yes. For the best experience, play The Binding of Isaac: Rebirth, which the developers still support.

Does the original have Wrath of the Lamb? Wrath of the Lamb (28 May 2012) is the original's expansion, sold as DLC. It added more than 10 bosses, over 100 items, over 40 unlocks, two additional endings and two optional levels.

Do my unlocks transfer to Rebirth? No. Rebirth is a separate game with its own save file and achievements.

Does the original have online or local co-op? No. Rebirth has local co-op, and the Repentance+ DLC (free for owners of the full Rebirth DLC collection) added online co-op in November 2024.

Why is it so slow on my powerful PC? The Flash engine is the bottleneck; heavy rooms slow down regardless of hardware.

Is the Rebirth story different? Rebirth retells and greatly expands the same story of Isaac fleeing his mother into the basement.

Sources

• Steam store page: The Binding of Isaac
• Steam achievements for The Binding of Isaac
• Wikipedia: The Binding of Isaac
• Steam news for The Binding of Isaac (Isaac Online / Repentance+ announcement)
• Steam store page: The Binding of Isaac: Rebirth