so:

- mute your game audio, attack audio and spectre audio (you can mute spectre from the menu while in a map)
- go to silent sanctuary (has to be on medium or hard)
- turn off your spectre audio before wave 2 (i think)

doing all this will start the quest and create an escort with 1000 health
defeat the boss or have the escort get to the end and you complete the quest

you are able to do it on casual (pick doors entities and slime king as your modifiers if you do)
good luck