Besides White 2 I would say that Diamond is up there as one of the "harder" (I use the term loosely) games in the series. I remember my last playthrough about a year ago that actually Lucian with his psychic types gave me a hard time, and that Cynthia was even harder. Nevertheless the most annoying part of the game, already mentioned in this thread, would have to be Mt. coronet simply because even with flash that thing was a pain to get through....