There is a difference between what triggers an unlock and what people assume triggers it. How to Unlock Forgotten Isaac is a good example of that gap.
One clean run beats five rushed ones, both for results and for your patience. Some conditions only evaluate when you return to a hub area, which makes them look broken. If the item is account-wide, you only need to do this once ever.
The short answer
The unlock fires on a specific condition rather than on progress in general, so aim directly at that condition instead of playing more.
What the requirement actually is
If something here stops matching what you see on screen, the game has probably changed a value in an update. There is a fast way and a safe way, and they are not the same thing. Check the collection screen rather than your inventory to confirm it registered. People often blame the game when the actual cause is a setting they changed weeks ago.
Most advice on this topic assumes you already know half the answer, which is exactly the problem. The approach below has been checked against the current version rather than a patch from two years ago. If something here stops matching what you see on screen, the game has probably changed a value in an update.
How to tell it worked
Anything marked optional really is optional, so skip it without guilt. Some conditions only evaluate when you return to a hub area, which makes them look broken. Unlocks that depend on a hidden counter are the ones that generate the most bad advice.
- Check the version you are running before following any step-by-step advice.
- Back up your save if the game gives you the option.
- Test one change at a time instead of five at once.
- Write down what you changed, so you can undo it if the result gets worse.
The quickest way to meet it
If something here stops matching what you see on screen, the game has probably changed a value in an update. If you are short on time, the first section alone is usually enough. Unlocks that depend on a hidden counter are the ones that generate the most bad advice. Start with the simplest option before touching anything that is hard to reverse.
Anything marked optional really is optional, so skip it without guilt. If something here stops matching what you see on screen, the game has probably changed a value in an update. Some conditions only evaluate when you return to a hub area, which makes them look broken.
Mistakes worth avoiding
- Changing several settings at once, then having no idea which one helped.
- Following a guide written for an older version and assuming nothing moved.
- Skipping the preparation step because it looks boring, then repeating the hard part four times.
Frequently asked questions
Does difficulty affect this unlock?
In most cases no. Difficulty changes rewards more often than it changes unlock conditions.
Can it be missed permanently?
A few unlocks are tied to a point of no return. If yours is, the guide above flags the last safe moment to do it.
Is there a faster method?
Usually yes, and usually it is riskier. The route above trades a little speed for a much lower chance of having to start over.
Bookmark this if you expect to look up how to unlock forgotten isaac again after the next update.