Hello again guys, I just wanted to let you all know, there isn't a "Killer King" achievement. I no it doesn't matter, but I just decided to check.
That achievement does exist. It is just a hidden one that is awarded when it happens.
The king move delivers the checkmate and is what gives the achievement.
So will we be thrilled with the answer to the question sometime today? Or will we be kept in suspense over the weekend?
The answer is kings cannot deliver checkmate. Like other people said, they can assist through discovered check or protecting the delivering piece, but they cannot by themselves deliver check or checkmate. Unless of course it's some variation or local rule that ignores the official rules of chess.