Ah.. I think I ran out of time by just a little bit.. ㅠ

There was a hidden quest that gives 20,000 gems for clearing stage 30, but it seems I missed out because I ran out of time by just a hair's breadth. ㅠㅠ I tested several weapons, and the sniper rifle is quite good. The ghost damage also adds a lot of convenience, so if you can get enough materials from weapon draws at the shop, I recommend upgrading to yellow sir grade. Then you'll be able to clear it comfortably. Make sure to max it out too..ㅠ