These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance: Mami's special attack. It was the same attack she used in the anime before she died. In the game it leaves her with barely any health, and can be prolonged to temporarily leave her a One-Hit-Point Wonder for extra damage.
Kyouko's barrier is basically useless... unless you're fighting Oktavia, in which case it's one of the few reliable ways to handle her.
Fridge Logic: Noted by Gesh86 in his Let's Play of the game: The most likely reason for getting the "Homura wakes up in the hospital and tries again" ending sequence is that Homuralost all her Soul Limit, as the rest get special endings.