The End?

The meta-achievement for the true ending: complete the Ending (kill the Corrupt Heart in Act 4) with the Ironclad, the Silent AND the Defect - i.e. earn Ruby+, 966201847 and 902745455. The Watcher is not required (the achievement predates her), so 779780464 is a nice bonus rather than a requirement. Each of those three explains the collect-all-three-keys route into Act 4.