My Time at Sandrock

This popped for me after winning the dance competition on easy difficulty.

The dance contest will unlock and take place over two days as you progress the story. Before taking place you will need to donate some food to be eligable for entry. I'd recommend going around and killing the rocket chickens and yaks to get eggs and meat, these can be turned in at the bucket stall by the oasis just before the guild.

Once the dance takes place go to the stall by the blue moon exterior stage. Interacting with the stall will give you a tutorial and allow you to select the difficulty.

It will advance time by 2 hours and take you to the mini game. Easy is fairly simple to complete and once you exit with your win the achievement should pop.