It's been a while since my last full playthrough, and I remember surprisingly few hard battles overall. I assume the sheer number of defeats drowned out the victories in my mind. Some of them, however, remain egregious, but they remained so only mostly because of sole-purpose mons (or stupid strategies such as collapsing the field on Luna's ace). So I can't recall when, or how, a long-standing member of my team singificantly contributed to a win.
Examples include how I used a (surprise, that's so original) Prankster Murkrow to disable most of single-Pokemon boss fights, how a Kli