A grid of coloured dots. Red joins to red, blue to blue, and no line may cross another. The first few boards solve themselves. By level twenty you are staring at the screen working out which path has to be wrong.

What makes it a real logic puzzle rather than a drawing exercise is that every board has exactly one valid arrangement. There is no partial credit and no lucky solve — if two lines cross, you have made a deduction error somewhere earlier.

The technique that works: start from the dots nearest a wall or corner. They have the fewest possible routes, so they are the most constrained, and locking them down eliminates options everywhere else. Solving from the crowded middle outward is how boards turn into knots.

This is the closest thing here to the planning half of Magic Sort — the part where you work out the whole sequence before touching anything.