You can move the King to do a discovered checkmate
Here's an obviously made up example
Hope it helps :]
With a bot? or Human?
Achievements only work with real players
Check my blog! How to get Killer King by BirdLikeChess
By eating a banana sandwich and playing on the toilet. Then get the king off the board and you win
I did it and I have killer king
I think u can also get it by castling