Hellya, thanks to a little bit of lazyness I didn't level my guys up and this guy dropped me in a single move.
As for bosses I managed to beat would prolly be the flying fortress defense system boss from FFV or that transformed commander guy from Xenosaga.
If I may say as for the easiest boss by expectation would be the Emerald Weapon in FFVII. I killed em in like 5 minutes. Two 4X cuts and a slash all all doing 9999 dmg. God I loved that game