How unlocks work
Progress in Isaac is stored between runs. Each first-time feat adds something to your game.
Those additions show up in later runs. A new item can enter the pool you draw from.
Boss kills add items
Defeating a boss for the first time often unlocks an item. That item can then appear on future floors.
So early runs feed later ones. A hard fight today widens your options tomorrow.
Character unlocks
Some characters start locked. You unlock them by meeting a condition in a normal run.
Each new character brings a different start. Trying them teaches you new ways to build.
Completion marks
A character keeps a mark sheet of the challenges it has beaten. Filling the sheet unlocks more rewards.
Chasing marks gives a run a goal beyond survival. It turns a familiar boss into a reason to play again.
Next: Which character to start and Repentance changes.