100% persona 2: innocent sin (psp) on retroachievements!
for the most part, it was pretty straightforward. a lot of story progression achievements and the getting all personas from specific tarot. mainly the hard or missable ones come from defeating bossing on hard mode, spreading all the 26 rumors, the god awful lvl 99 grind/grinding to have the mutation personas change forms (even with alice in the abandoned factory it was still a slog), fool card grinding (you only need 10 and there is a guide on the retroachivements site to acquire them) and that godforsaken persona thief dungeon with the pitfalls.
all that to the side, if you’re gonna go for this yourself, play on hard mode. there isn’t too too much of a difference. rotate saves! the choices you have to save your friends or let them handle things themselves have separate achievements so to not have you 2 two play throughs, save before you enter a dungeon on a new slot. pick the let your friend handle it themselves option (key for gaining new persona), and play until you leave and save in a new slot. reload the save before you entered the dungeon and choose the save your friend option, fight, and you’ll unlocked the achievements to move on.
good luck!