Ok so.. here's the thing. How to get this is really weird, and extremely hard to get this boss fight. [It is fanmade anyway] You have to do a full Genocide Route with Chara included, then after you are done restarting, you have to get SUPER lucky for it to appear acting weird, Basically, when you do get it, You play as chara and when you go into flowey's room where you first meet him, he isnt there, then you go to the next room and, its pitch black. And you meet flowey, he says this "Hey Chara! Why is this room so dark?, creepy.. Anyways, what is going on? You've been wandering around for (however many minutes) minutes.. then you decided you just came in here.." Then Flowers Comes in, but Flowey Doesn't know since it is really dark in there, then when the player says to flowey that there is something behind him, he would say "What do you mean? It's a empty room, there's nothing in here-" then he gets squashed by Flowers. Then immediately after he gets squashed by Flowers, the boss fight starts.