Top 10 Hardest Bosses in the Paper Mario Series

I found this boss to be very difficult. It took me roughly seven tries over a span of three days to defeat her. However, what I still laugh about today is that I had such a hard time beating her, but I finally finished her off with a party member. With whom? With Goombella. I guess she was of some use after all.
In my opinion, the toughest boss in the Paper Mario series. Some would argue that Bonetail is tougher, but I personally found The Shadow Queen to be harder, as her attack pattern is way harder to predict. She can also attack multiple times with her hands, while Bonetail can only attack once.

People voted for the Shadow Queen because if they thought she was hard, then they were probably less likely to have even gotten to Bonetail. Bonetail is statistically the hardest boss. He has 200 HP, higher defense, can do about 8 damage per normal attack, inflict status effects, and can only be dealt raw damage or burned. He can also heal himself for 20 HP.
This would be difficult enough, but the main cause of difficulty here is that you have to beat him directly after the 100 trials with no save point. You can heal yourself with any items that you have prior to the fight, but you probably don't have any left because of how hard the trials were. Excellent challenge though, 10/10. Shadow Queen's hands are easy to deal with.

This boss was not only hard, but had an amazing theme!
Which game, PM: TTYD or the original Paper Mario? I don't know what to say about the original, but in PM: TTYD, just kill Kammy Koopa, and you're pretty much in for the win.

It is taking me days to beat this guy! He keeps on creating barriers after every turn!
Gale Force and Fiery Jinx are useful.
This was definitely a very challenging boss to beat. My friend kept jumping in front of the TV, and I ended up having to fight them. I was not prepared, and I lost all my Life Shrooms and Repel Gels. Definitely a fun yet extreme fight.
OP. Nothing else. A minimum of 27 damage per turn - this is easy death. Luckily, this fight is optional. You face him by losing in one of Bowser's Castle's puzzles.
They just made this boss fight as an alternate game-over screen.
Alternating between strong attacks from Mario and all-foe attacks from your partner (Lakilester's Spike Storm, Sushie's Tidal Wave, Parakarry's Air Raid) is a very solid strategy. It decreases attack and prevents him from permanently healing back his health.
The most annoying part about this boss is when he's down to 6 HP. He causes an earthquake that deals 15 damage! I used the berries, but the Tuff Puffs kept getting me below 15 HP. Hardest boss in Paper Mario. (But I still need to fight The Crystal King.)
Guys, I recommend you use the star power that decreases the enemy's attack (best when more Tuff Puffs are on the field). If timed well, they will deal no damage or just 1 or 2 damage. P.S. I spammed Star Storm on him at first.

My almost biased love for Super Paper Mario can't stop me from calling most of the bosses fairly easy, but there are exceptions. Count Bleck, Francis, and most notably, Shadoo. He turns into dark clones of Luigi (even if he hasn't joined you yet), Bowser, Peach, and Mario in that order.
You're going to hope you had some healing items saved up from the first 99 floors. Even spamming Bowser's flame doesn't make this fight easy - it's the ultimate test of your SPM skills.
Oh yeah, did I mention that ALL of his attacks do 10 damage? Except Bowser, of course. He does 20!

If you use Luigi, it's not too hard. But with anyone else, I wish you luck.
I think this boss is a girl like Hooktail, and she is as hard as Count Bleck.

God, this brings back two years of frustration. The ice beam finished me every time. I never managed to beat him until 2011.
I found this boss much harder than Huff N. Puff.
I could never time the ice beam block right, and the Crystal King ALWAYS healed literally the moment I landed one of my attacks.
Their health and attack strength are greatly increased, and the fact that Doopliss can copy your partners makes this battle tough - especially if he copies Bobbery.
The Shadow Sirens are a tough boss.
The Newcomers

I beat it once by chance by using all the power-ups I had. The first part is simple enough if you know their powers. The second is a breeze. The third is no joke - IMPOSSIBLE.

You'd better hope you have Defend Plus badges, a good guard/superguard, or HP over 30 once Crump launches his cannons. It does 30 damage!
My favorite Mario character! Gloomtail is undeniably hard as one of the Chapter 8 bosses in The Thousand-Year Door (wow, I made a pun). He has 80 HP and access to most of the attacks he shares with Hooktail and Bonetail, such as their Stomp and Bite attacks. However, he has his own breath attacks and one unique attack that only he can use.
He has Poison Breath, and his charged breath move, Megabreath, is his signature move and one of the strongest boss attacks in the game, if not the strongest. His secret move, which neither of the other two dragons have, is his Earthquake attack, which makes him really unique. It's basically like Magnus Von Grapple 1.0's Earthquake attack, where it penetrates your defense, but Gloomtail doesn't bang his feet and arms on the floor like crazy to do the attack. Instead, he jumps up, and when he lands back down, it triggers the attack.

This is the only Paper Mario game I have played, and I haven't beaten the pits yet.
If you use Mario, this boss can be pretty tough.
It took me a while to figure out his weakness.
Grodus was actually pretty underwhelming to me, but this fight was where it really kicked up. I recommend taking out Kammy Koopa before even bothering with Bowser.

I beat Shadoo on my first try. This guy? I'll pass. I think I'd rather defeat all four of Shadoo's forms simultaneously.

I did not know this boss was coming in Chapter 6 - it scared the living life out of me.
20 HP, Mega Rush, Super Charge, and Power Bounce are all you need for this fight.
His attacks are absolutely devastating. I loved this fight, but it was hard!

It should be noted that Gale Force completely removes Cortez's weapons from battle, while Fiery Jinx only knocks them out for two turns.
I used all my Ultra Shrooms on this boss. It was my first attempt, though I did manage to beat him on my first try.
Cortez - what?! Sounds like a diss!
6 defense, 70 HP, takes your partner out for 3 turns, immediately gets back up and attacks after you flip him, and finally, can do 10 damage.
Unlike any other boss in this list, if you don't know the correct strategy, you will lose.
In short, less of a boss, more of a puzzle. The precursor to Sticker Star and Color Splash.
Strategy for beating Kent C. Koopa: Use Lullaby every time he wakes up, and just keep attacking. Use FP attacks to go faster, or just use normal attacks to save FP. Have Mario focus so you can always use Lullaby.

The bosses in this awful game were like vacuums - you use ALL of your stickers! This guy is no exception.

The spider form is pretty hard, but the fight with her in Sammer's Kingdom is definitely the hardest.
Mimi is pretty hard in her spider form (and disturbing), but her second battle in normal form is the hardest.
She is quite challenging because you need to hit her head, which is quite high.
I literally couldn't pass this fight as a kid, even though it was my favorite back then. Not to mention, the boss himself and the theme are cool as hell.
Ice Power is your best friend. It makes the second phase ten times easier.
This took me like four days! And when I thought I had beaten him, his second form appeared! I screamed!

This guy's pretty hard since you can hardly go anywhere on screen without getting hurt. Bowser helps immensely, however.