Keys are shared by the active run. When a hero carrying a key approaches a locked door, that door opens and one held key is consumed. In multi-door stages, order matters.
Match keys to doors
Count the visible keys and doors before moving. A nearby door is not always the correct first door. Opening the wrong one can leave the important route locked.
Keep the team together
Before crossing a door that may separate the level, bring all required heroes close to it. Open the door only when the next area is ready.
Safe key handling
Collect difficult keys with the hero best suited to the route. Since keys are shared, that hero does not need to be the one who opens the door later.
Play and practice
Use the playable game on the home page to apply these techniques across all 20 levels.