Logic Masters Deutschland e.V.

Basic Hex Masyu rules: Draw a single, non-intersecting loop that passes through all cells with circles. The loop may go straight through a cell or make a turn resulting in a 120° angle (no sharp bends). The loop must go straight through the cells with white circles, with a turn in at least one of the cells immediately before/after each white circle. The loop must make a turn in all the black circles and must go straight in both cells immediately before/after each black circle. Black cells are cells that the loop cannot pass through in both grids.
Evil Twin rules: Dotted circles in both grids represent where either a white or black circle must go. If a white circle is on one grid, a black circle must be in the same position on the other grid and vice versa. Dashed cells in both grids represent cells which the loop in one grid must pass through while the loop in the other grid cannot pass through.

Example