I FINALLY just beat the Shroob Princesses yesterday! It took me the entire nine-hour drive from Florida. I was only at level 18 or something, so it took forever. I would shut the DS for 15 minutes or so to take a break, then I'd turn it back on.
It took me months to beat Cackletta's Soul, partially because I had to start the game over after getting pummeled by Ludwig, and then I beat her/it once after getting to her/it again and shut the game off because I was an idiot and couldn't find my way out of the castle, so I had to redo the fight a third time before I was actually able to see the ending.
Honestly, I love the Mario and Luigi RPG games, but they have the most ridiculously difficult bosses. It's almost not even fun to play them. They are rewarding to beat, though.
Huff N. Puff is only hard if he keeps replenishing his HP and there's an easy way to make it less effective. Crystal King is way harder since he can replenish 20 HP and he can freeze Mario.
The final Bowser fight is rather annoying considering he can replenish 30 HP and you have to sacrafice every other turn with Mario to use the Peach Beam.
In TTYD, it would have to be the Shadow Queen since she can attack you 3 times per round and her HP is in the triple digits.
Fighting Bower and Kammy Koopa can be a bit tricky if you didn't level up off Grodus.
For Mario and Luigi, I find the Memory Bros. to be hard since they can revive each other.
For Bowser, I'd say Peach's Castle, specifically the second phase where there's two black holes.
The Chapter 6 fight with Mimi in Super Paper Mario was very hard for me. I did it on my second attempt but then died on Brobot L Type and hadn't saved. It took me ages to finally beat her again. Trantrox also took me a while at first.
When I was little and playing Super Mario Sunshine, me and my older cousin despised the Manta Storm. Having to dodge the separated medium sized mantas was literally the worst and we stayed on the treetops for eternity after eternity. I even remember when I cleaned the entire beach to make the battle easier, and then the boss had to go and make everything dirty again...
But now after a few years, I can hold my own against it. It can be annoying sometimes, but I won't get angry to the point where I want to slam my controller against the screen and cry.
Well, I may seem silly for this, but that Caterpillar in the Vim factory in Mario and Luigi: Partners in Time was so hard, I just gave up for a little while.
The part where Mimi turns into a spider in Chapter 2 in Super Paper Mario was pretty tricky for me. It took me like 7 tries to beat her!
