I realized I haven't actually gotten any credit towards this feat, which says to "attempt to inflict potency down 40 times." In other words this isn't a case of positively having applied it, just that it needs to be attempted. So I was surprised I had zero points towards the fear because I was certain I had used GMY at some point. Oh well, I decided to start grinding that one out and jumped into a fight with JML lead and GMY on the squad. Yoda's basic says "deal special damage and apply potency down for 1 turn..." so this is simply do the basic, apply potency down, right? Well maybe
A full fight later and between attacks and assists I had 4 basics done by GMY... and zero points towards the feat. I ran the fight again to see what was up and once again, four basics, zero points. The only thing I can come up with is that I had too much offense boosting going on and I believe every attack was a killing blow, so that's why I wasn't getting the credit for the potency down. I then took off some discs and tried it again, this time getting credit when I didn't kill an enemy.
I'm not sure if that's intentional or not, but it certainly isn't intuitive for the game mode. I just wanted to get that out there in case someone didn't realize this when attempting the feat. It appears at the very least for this feat that killing an enemy does not fulfill all steps on attacks