You're more than welcome! I do enjoy bouncing idea regarding game design, so I have to say, my pleasure!
I definitively can see how doing more damage on critical break would make the combat flow better ; my main grip with it is it didn't felt that rewarding with how many HP mob had ; I was just looking at it as a bonus if you managed to save all of your power more than something to really aim for. Definitively happy with that change!
Somehow, I wonder why I did not expect than protag would get a bit mouthy with other body too - it's in hindsight pretty obvious that is bound to happen, and indeed having different body doing different things make sense. I'm a bit concerned on how it would affect the narration (partially because I liked the flow between maggot and protag (which doesn't mean other character would not be great to have as brain-friend) ; and partially because if you have the choice to which body bring at which part of the game may lead to an to a pretty huge number of alternative dialogue to do)
As for the holding card mecanism, IMO anything that would increase player choices would be an interesting improvement - currently the combat is like one minipuzzle after another, each disconnected from the last - kinda like you have a hand, have to react to that, and that's only what agency the player have on combat, which is not much.
Anything that allow how you did a puzzle affect the next one (like, which card you did held, which effect you did not break, or any ressources sytem (like mana) you used or not) may make the combat more engaging, because it gives more agency/choice.
I'm not sure I understood how these hidden defense slots are supposed to work ; is it like, defense slot with a ? on these and you need to use any card to show them?
If yes I do think that mecanism may be on the frustrating side: I can see myself burn a card to reveal it and now don't have the right card to critical break it, which would feel a bit too RNG heavy and may not be that fun. As a gimmick for specific enemy, it may work at making them (frustratingly) memorable, but I hope it either won't work as I expect it to do or not be a recurring mechanic.
You're welcome again o> And thanks for taking the time of explaining a bit on what you're aiming for!