Could someone take a look and tell my why this pretty simple pack wont work?

Ive been messing with this for a better part of 6 hours.... even consulted chatgpt💔 basically i have the better end installed. which doesnt spawn the dragon until you get near it, and when it does spawn it instantly dies to let what the actual boss is supposed to be spawn, all im trying to do is have the dragon instantly die, and then spawn a mob once. so people couldnt catch the same shiny legendary over and over, first come first serve