Chest
Chests are treasure containers that hold various items based on what tier of dungeon is completed. A compiled list can be found here, with the various drop rates per tier (use the find feature CTL/CMD + F and type in CO2, for example).
🗝️ Dungeon Chests
Dungeon chests appear at the end of a Dungeon after defeating the final Boss, and are free to open.
(Chests previously cost Yoku energy per dungeon tier — an energy type that has been removed from the game.)