Phantom Thief's Notice

It seems you're having trouble with the Phantom Thief event progression. You should be able to get rewards by meeting certain conditions or clearing stages, but checking the in-game announcements is the most reliable way to find details. I made mistakes before, so I really want to help you out this time... Hou!

It's completely a game of luck. If you choose a direction, you get the gem determined by the roulette in that direction. Each gem has a different point value. The mirror ball allows you to collect all gems on the board. Stopping on an arrow lets you collect all gems in the direction the arrow points. It's something like that. Since luck is a strong factor, I think it's good to actively choose the direction with the mirror ball.