User blog comment:The Milkman/Shades of Purple/@comment-5287758-20120930050555/@comment-24174486-20121002013817

"But the star/god/whatever child is a contrived, sudden solution. He is introduced in the climax, the climax."

No, you're told about the Catalyst by the Prothean VI, Vendetta. You're told exactly what role the Catalyst plays in the ending, and it does exactly what you were told it would do. The fact that the Catalyst is an AI which created the Reapers (the existence of a creator of the Reapers is also foreshadowed by Vendetta) changes very little about the role that you were told that the Catalyst would play. The only things that the Catalyst adds are the reason for the Reapers' existence and the Synthesis option. And Synthesis doesn't exactly come out of nowhere, either—it's combining organic and synthetic life, like you've seen the Reapers doing repeatedly throughout the series.