Explaining Heroic Alleria (Crown of the Cosmos) to myself

A product of my own research and experience on trying to figure out this encounter on heroic. I found it helpful, so thought maybe others would also. EDIT: At 17:25 I say "when Alleria has low health" It should be, "when the simulacrum has low health" The Dratnos video I used to put this together:    • Heroic Crown of the Cosmos Guide + Commentary