How do I win a round?

Pop every bubble that is not already flattened before the timer runs out. The bubbles that start grey are already popped · you only need the puffy ones.

How does difficulty change it?

Three things move at once. Harder rounds leave fewer bubbles pre-popped (more cells to clear), give you less time per cell, and grow the sheet · from a 5×4 grid at the easy end up to 10×8 at the hardest. A high-difficulty clean clear is a real scanning-speed achievement.

Is the sheet always the same?

No · the pre-popped pattern and the time budget are derived from the round seed, so each round looks different. Sharing a save code reproduces the exact sheet · useful for "beat my round" challenges with friends.

Visual scanning under time pressure, plus the fine-motor reflex of tapping rapidly without missing a cell · the same skill bundle that show up in arcade puzzles and Whack-a-Mole. The brain-training angle is that scanning + reflex degrade noticeably under stress; sustained practice keeps the loop tight.