The propose of this post is adding the hardest and the easiest boss you have been battle
in all the titles that you already played, you can add many as you can,

Hardest

1-Kaiser Sigma- Mega man X 3 
 Everyone who played X3 knows the Sigma of this game is one of the hardest sigma of the video games
the reason is the size of the weak point compared with his body size and his attacks are devastating

2-Phalanx- Demon's Crest
Like I say every time, Capcom wants to make our suffer with their impossible challenges
Demon's Crest a not well know game is a hard game and you need a good equip to destroy it and 
his final form

3-Yiazmat-Final Fantasy XII
This boss is a very strong not only for the attacks is more for his Hp
For give you an Idea he has over 5 millions of Hp and have reflection
that means if you use an cure he will absorb it and recover all his Hp I take
to beat him like 19 hours of battle, is true with out the right tactic you can take hours even days

4-Dark Samus (Hyper mode)- Metroid prime 3
this is one of the hardest boss what I ever fight 
the difficulty compared with the normal mode is extreme have more resistance, attack faster
and have a lot more defense

Easiest

1-Glass Joe-Punch out
From the classic punch out of the NES have this unless character is the equivalence of an human punching bag
don't have any good power expect fall like a sand box, is true 5 year babies can beat him with the closed eyes

2-Very Gwanty-Donkey Kong country
this boss is easiest of the game their moves are slow and easy to avoid and you can beat him with no much trouble

3-Cloud N. Candy-Yoshi Story
is not only easy I laugh with his presence this boss is really easy, for beat it you only need to 
eat him also you recover all our Hp eating a piece, is slow and if you can't defeat him is because you don't know how play

4-Bob the gold fish- Earthworm Jim
boss? This is a joke for the game because you only go to the fishbowl
and eat him, but I laugh for a worm who eat a fish

Easiest.

Cryatalis NES
DYNA All you need to to is equip the warrior ring and the crystalis blade will do the rest.
a recent discovery about 2004 is when I first beat this boss but this was the fourth game I played as a little kid. This was the game that sparked my imagination and finishing it was truly satisfying. This boss has a lot of constant attacks to throw at you you can dodge or use barrier but the best thing to do is what I said above.

Batman NES
Firefly need I say more. He has a clear easy pattern to recognise and all you need is the splitting weapon and you got him without much damage.
this was an early one from my childhood and I was not very bright back then. If I could beat him anyone could even back then he was the easiest boss I ever faced

Star Fox Adventures Game cube
General Scales. Seriously. You don't even have to fight him. All you have to do is wait and he defeats himself.
to this day I never understand this boss. I loved how I didn't have to do anything and he defeats himself. 

Ocarina of time
Gohma. Shoot her in the aye and jump slash. 6 times while stunned.
this was my favorite boss in OoT I liked it.it was simple and fun not to mention I was creeped out by her as a kid. First boss on my first new game system of my life.

The hardest boss I've faced in a while is

The bosses in Killer is Dead are insanely difficult.
The Crash Bandicoot bosses can be quite easy.

Hardest:

The final boss in Dragon Warrior 6. Even with savestates, this game is nearly impossible to beat because the final boss is so hard.
The optional bosses in Final Fantasy V and VII. No wonder they are optional; they are harder than the final boss!
The Final Fantasy III bosses you have to fight miniaturized. That takes away the possibility of physical fighting
Odin in several Final Fantasy games. The fight is timed (explicitly or not), so overleveling is usually necessary.

Easiest:

Yu Yevon in Final Fantasy X. I don't know if I was simply lucky, but all my characters were on auto-resurrect each time I fought him.
Any Final Fantasy X boss once you get the Magus Sisters. They are so overpowered that you can crush anyone.
Bahamut in many Final Fantasies. Once you figure you need to cast reflect, he's a piece of cake.

The hardest boss I have ever faced in a game that I've played extensively would have to be Lucifer in Shin Megami Tensei IV. I mean I can get to his second form by reflecting his attacks but he just obliterates my entire party anyways. I can only reflect three of his attacks since the rest of them are either ailment giving or are special like returning a demon to your stock. Now, I turned on "easy mode" at the Kenji boss fight, which was also a difficult fight, so I can only imagine what Lucifer would be like on normal difficulty. Also consider that he can take three actions during his turn, meaning he has three ways to devastate my party. he could remove a demon of mine from play, damage my entire party and cause them to panic, which means i can control them, can't control, or they can't do jack, and he could reduce my entire party's current health by half.

The Easiest boss is got to be the chemical plant boss from Sonic 2 This boss is so easy that I stay to the right and jump that way i keep hitting him The hardest boss is got to be The final boss in vectorman I know that sounds crazy but its true I had to use cheats for this boss

the easiest boss are in the mario and sonic games.
but sometimes it could be hard

One of my easiest bosses to beat should be...



Bowser (-:
From mario nes



The hardest though...


Is giovany the boss of team rocket
In one of pokemon's rom hacks

Hardest boss - Yellow Devil from Mega Man: This boss is very hard when you first play the game, as you will game over on him the most. He is very easy though when you learn the pause trick with the Elec Beam

Easiest Boss - Toad Man from Mega Man 4: All you do is shoot move when he jumps, and he will never be able to get any hits on you whatsoever.