Eelektross anybody? No one? Oh. Well, I had serious problems facing that one when he was on Cynthia's team. Probably because I kept hitting it with leaf and electric attacks cuz I thought its water type xD but seriously, I found him incredibly hard.
Had problems with reuniclus as well, I had my whimsicott ready and tried toxic. And then i found out, for the first time, about that magic shield thing. By then he had gotten himself ready and destroyed me.
I've never had problems with volcarona or excadrill tho.... but i thought ghetsis hydreigon was stupidly strong. I almost thought i have to retry him b4 i beat it.