Secret of evermore is the only boss i can think of at the moment that i felt was unessicarly challenging for being the first stinking boss of the game...though im sure there are certainly others (Then again can ANY first boss be considered hard? )
Yeah, smurf Thraxx. It's not like they tell you to grind your alchemy out the wazoo to actually have a fair chance. At least it's impossible to die during the end boss though. Barrier + Energizer for the freaking win.