I originally played the watcher and got this ending, however upon replaying the campaign, I cannot seem to trigger the ending. For reference, I believe I have rotted every location necessary.

The only regions I can see on my map not rotted are ancient urban, daemon, and shattered terrace, which were the 3 I recall cannot be rotted. Are there more conditions I am missing? I activated 4 portals in the throne room, but I'm not sure what else I'm missing.