asically a tapping game. Tap to kill mobs. After a while boss mob spawn which have to be killed within x time if not they escape and you have to try again.After you kill mobs you gain crystals which you can use to upgrade your crab and queen. Same you gain offline rewards.
https://youtu.be/ixNTILONKT0 Its similar to those games where you just avoid obstacles until you die. You get orange orbs in the game to buy power ups You get notes along the way to unlock new stages it seems.