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.
YMMV: Grief Syndrome
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.
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.
That One Level: The other four levels are a fairly straightforward progression of more and more powerful Familiars and Witches with harder to avoid attacks. Kirsten, however, has a Bottomless Pit and other stage-hazard-filled Barrier/Labyrinth (where none of the other Witches use stage hazards, and enemies which love to act as Ledge Bats.
... and Fridge Brilliance when you realize Sayaka is the ideal character choice for that level.
Becomes a Goddamned Boss when you learn how to deal with her Familiars, realize that the final boss fight doesn't actually have any decent attacks besides said Familiars, and learn how to hit her real body instead of the Doppelgänger Spin. Hint: It's the blue monster face. There's always one, and only one, and it's the real her; only hits to it damage her.
Tier-Induced Scrappy: Mami and Sayaka, for the inverse reason: Mami for being too weak compared to the series, Sayaka for being too strong.