ff1 don't know
ff2 none
ff3 don't know
ff4 ashura
ff5 atomos
ff6 wrexsoul
ff7 none yet got to ice area lvl 55
ff8 still have to beat and learn card game
ff9 still need to beat in storage

ff4 ashura I did not use reflect

ff5 i went all out

ff6 you don't know who he will possess

ff7 i pwned matra master i don't see why people say he is hard

ff2 i only had trouble with gigas

ff3 i need to beat it
ff1 i found all bosses easy

ff8 at assassinate the sorceress
ff9 after gizamaluke's grotto and dagger and stenier part after that

1.-Never got far enough to get to any boss other than Garland, but you could kill him at lv.1
2.-This dude who unlocks mythril when you beat him
3.-Big Rat, a boss you had to fight while mini
4.-The second of the four elemental fiends, couldn't remember his name. The water one.
5.-That one dude made of fire on the Fireship? Hate him.
6.-Don't remember having trouble with anyone.
7.-The boss of Red Canyon was a pain. (phoenix down anyone?)
8.-Diablo. Saved, then fought him right away. Bad idea.
9.-Magic something #2. Was really hard for me.
10.-The boss at the end of Gagazet caves gave me a ton of trouble because of curaga.
X-2.-Angorea-Maru. The one like 1 million hp. Literally. Took me like an hour to beat.
11.-Never played
12.-Earth Wyrm. Showed up for no reason at all and can inflict like 10 status effects at once.
13.-Vanille's edolion. It has a really long name and is really cheap.
4 heroes of light - Stupid bird on top the big tree place.
FF CC-Boss of the mansion 3rd time around. Really hard solo.
FF CC RoF-Final boss. He deals like 200 damage.
FF CC EoT-Ruins boss. If I remember, he was tough on hard.

The hardest bosses I've ever fought was Yiazmat and Gilgamesh in FF12, they whupped my @$$ like I owed them money. They made sure that my torment was legendary, much so that I watched my hair fall out from all the stress and frustration I had to endure.