OK I've just done another battle with Mr Scorpion and fared better this time, used maybe 4 potions and not 15 😂 I changed the setting for target switching to d pad rather than right stick which worked much better for me, as I like to rotate the camera when locked on to get a better view, but that kept switching my target (eg when going for the legs). Used Barret's Overcharge a lot and made sure to keep MP topped up to use Thunder, and then get Cloud in for some specials to try and build stagger. Still didn't manage to stagger it often as every time I get close it has a fucking change phase cutscene and resets the gauge lol. And I got a limit right at the end and landed Cross Slash as the killing blow which felt good.