Twenty-five linked lights
Lights
Out
Press one light, change its four neighbors, and find the sequence that leaves the whole board quiet.
One press changes five
Think in
crosses.
Pressing a cell toggles that light plus the cells directly above, below, left, and right. Corner and edge cells affect fewer neighbors. Turn all 25 lights off to finish.
Every new board is created by applying a sequence of legal presses to a solved board, so it always has at least one solution. The generation press count is not presented as a difficulty rating.