How to complete the Festering Secret quest in Phantom Blade Zero

The Phantom Blade Zero Festering Secret tasks you with helping the Mandate clear out some warriors that have gone a bit evil due to Transcension. But you'll come up against some major obstacles along the way. The first being that you need to beat a nearby boss to be able to break the chains to the courtyard. The second being that you need to get a key for a gate which you also can't reach until you defeat a different boss. To clear up how to complete this quest, I've laid out all the Festering S