1st Step: in night 1 click in where the key is just bright up the image of night 1 minigame and click in spot where key is! Then click on the message window until its showing a chest and drag key into a chest. After that it opens and shows a code 9-5-7
2nd Step: after gettingthe code go in night 7 aka custom ight and beat it on any difficulty! even without character's and when you get to chest press each lock from left ot right , that many time how you seen in code click on left lock 9 times , on middle one 5 times and on right one 7 times, after it the chest will be unlocked and katheley will pop up out of it!
3rd step: click on katheley head in main menu multiple times until you hear a sound and katheley head near "EXTRAS" Button if you do it you will unlock her head .
4th step: after getting her head go in night 6 and do normally like you do in that minigame, execpt golden leopold will reset timeline to get rid of incindents tragedys and bad about agk studios , ending its nightmare then talk to mallie
5th step: just you can read katheleys dialogue! Just its a undertale fight dodge her knifes press space and hit her to get 1 of 4 main classic fnatas games ( there were 5 games and tcotas was canon to main 4 until fnatas 5 appered! so now tcotas is not canon! ) after that you just beaten the game!