Diagonal selection is not available yet, regression bug.
From our help, Difficulty levels:
Easy: Neighbor highlight is available and diagonal selection (in case of square board layout) is possible on all game levels in this mode. Time adjustments and score limits are the mildest.
Medium: Neighbor highlight is available on the first 5 levels. Diagonal selection (in case of square board layout) is possible on the first two game levels in this mode. Time adjustments and score limits are thougher than the Easy mode but milder than the Hard mode.
Hard: Neighbor highlight is only available on the first level. Diagonal selection (in case of square board layout) is not allowed. Time adjustments and score limits are the hardest among all modes.
Diagonal selection is not available yet, regression bug.
From our help, Difficulty levels: