MoF for me as well, in particular VoWG. That one comes up a lot. For whatever reason it's non-spells that are more likely to get me, and make my head ache when I remember what learning them was like: Marisa in Stage 4 of IN, Orin, Patchy - all their non-spells were very painful.
Most recently, been playing ISC again after about a month hiatus from any shooters. For whatever reason, I persisted to use the Umbrella against School of Fish, despite failing at best, even timing it out, which I don't even remember doing when I first played it. I don't know how many times I kept using it before switching to the Toy Camera and getting it in 1.