This is a system i created for my RPG Maker game: Eos
It consists on a mini-game where you have to repeat the same color pattern the game generates, by combining 2 colors using the wooden discs at the center.
If the player succeeds, he gets what was inside the chest. If not, he is given another chance to try.
It can also be adjusted in 4 dificulties, which increase the number of colors to memorize and the time. The dificulty will vary depending on the content
EDIT: made a video of the system: [link]