There are many Special Chest types in the game. Each type has an immediate effect when opened.

You may set one type of special chest in your loadout before beginning a quest. Your selected special chest can replace regular chests.

Quests have a ~10% chance to have a Locked Chest. If your quest contains the chest, a sign will appear that says "There is a secret on STAGE_NAME!".

When you get to that stage, look for a sign with hint or suspicious item.

If hint sign says a password, such as a sequence of numbers:

Password

Action

Customer's:

Activate a Stranger with a coin price equal to or higher than each of the code values, in order

Chorder's:

Chord the indicated cell values in order (you can still manually open cells between the different chords)

Shopkeeper's:

In an item shop, click on the indicated item for sale in order

Monk's:

Lose items* from the indicated inventory slots

Moneybag's:

Collect coins or diamonds in the order of the passcode

Wizard's:

Use magic items to target areas with each of the indicated total cell values in order

*Duplicate consumable items are consumed in order of first in inventory, no matter which one you click. This makes Monk's password more difficult.

If that stage have items but not the sign with password, obtain the key by interacting with an object or cell.

Item

Action

Bagman:

Pay the bagman multiple times

Barrel:

Click it

Meteorite:

Use it

Nomad:

Buy from the nomad selling "keys"

Obelisk:

Succeed in the obelisk's challenge

Sanctified Cell:

Target with magic item

Mystic Statue:

Enter to reveal the "secret" inside

Spawner:

Activate it until it breaks

Wishpool:

Activate it when its charge is 3 or more