I know the weapons are obviously the hardest for anyone, I was thinking about regular bosses or some minor enemy that is really annoying for that part of the game.

Here are some of my enemies:

Master Tonberrys and there stupid Everyone's Grudge thing with its really annoying low pitched noise followed by the high pitched DEEE and a dead party member. Thanks for the Ribbon and Elixir though, sucker.

Anything that can kill you in one hit or change your status.

Those things by Cosmo Canyon that make you only do one damage when you attack.

MATERIA KEEPER!!!!!!!!!!!!!!!!!!!!!!

*sorry about the caps, it so anoyed me when i couldnt beat it first time*

The master tonberries, the behemoths in the northern crater and the grand dragons (which killed me a bajillion times trying to get the dragon force enemy skill).

also, that boss in those ice caves that had ice and fire attacks. I died a few number of times the first time I played trying to beat that thing.

Torberry >:O Those were definately the most annoying to me! Unless you're invincible and can kill them before they can attack with everyones grudge. =)

Those Giant, big mouth Plant/Tentacle things with all the staus effects, Malboroughs I think...They continually killed my level 99 party

ALL THE STUPID VILLIANS WHO ALWAYS COME BACK!!!!!!!!!!!!!11

The Master Tonberries, because they are pretty annoying when you first enter the Northern Cave unless your party is maxed out. And really any monster that can put the confusion status on you. I hate it when my characters are confused. :(

Materia keeper and Malboros

Madouge - That red thing you fight near Icicle Inn. Its really easy but you can't use physical attacks on it, they always miss.