Something I've never bothered to find out previously: when completing challenges in order to level up mastery, do you have to complete the entire mission in order to have any challenges you completed during that run count? Or are they marked as completed and added to your xp from the moment only the challenge is completed?
I want to try and finally master Paris, but I'd have to run the entire Showstopper mission a bunch of times to try and do this, which sounds pretty repetitive.
You do not have to finish the mission to count as completed or get the XP. Basically what I did is save before killing a target reload then kill them a different way and repeat.