Mega Man X/Bosses

Note that you can defeat every single boss listed here without the need to obtain any Heart Tanks, Sub Tanks, or upgrades (however without glitching the game, there's no way to legitimately reach the end of the game without the leg upgrade).

Vile in Mech Armor
This is a storyline battle, so you can't "win" (Vile is invincible). Once your energy meter drops below a certain point (at around four or five left), Vile will start shooting "energy nets" (glowing yellow orbs) at you, making you unable to move. Once you're hit by one, the story will proceed and the level will end. Keep in mind that if you're hit enough times before being trapped by the "net" you can still die; so try and get hit.

Chill Penguin

 * Weakness: Fire Wave
 * Weapon Received: Shotgun Ice

Chill Penguin can shoot ice cubes across the screen at you as well as create miniature penguin ice sculptures. When he grabs the handle on the ceiling, he'll create a snowstorm and the sculptures will slide across the floor. Chill Penguin can also dash across the floor. The Fire Wave will make short work of him; just be careful when attacking as the Fire Wave has a very short range.

Spark Mandrill

 * Weakness: Shotgun Ice
 * Weapon Received: Electric Spark

Spark Mandrill will frequently jump across the screen and try to crush you. He will also dash at you, swing across the ceiling and try to drop on you, and shoot Electric Sparks at you. Shooting Spark Mandrill with Shotgun Ice will momentarily freeze him and do significant damage to him. If you shoot Spark Mandrill after he breaks out of the ice and right as he lowers his arms, then you won't give him a chance to move. You can repeat this timing with Shotgun Ice to defeat him easily.

Armored Armadillo

 * Weakness: Electric Spark
 * Weapon Received: Rolling Shield

This battle is made much easier if you shoot Armored Armadillo with at least one Electric Spark; it will electrocute him and cause his armor to fall off, making it impossible for him to block attacks. Armored Armadillo will attack by shooting Hadoken-like fireballs and rolling across the screen at you. Simply move out of the way of his rolling and jump over the fireballs (or climb the wall) and Armadillo is a pushover.

Launch Octopus

 * Weakness: Rolling Shield
 * Weapon Received: Homing Torpedo

Launch Octopus has two main attacks. He'll either fire torpedoes at you or leap across the screen and create a whirlpool vortex to pull you towards him. If he grabs you during this move, Lauch Octopus will begin to drain some of your energy and regain his. This can be countered by either dashing away from the whirlpool or by cutting off his extra tentacles with the Boomerang Cutter. By using the charged version of Rolling Shield, you can protect yourself from torpedoes, but in order to hurt Octopus you must get very close, leaving yourself open to attack after the shield evaporates.

Boomer Kuwanger

 * Weakness: Homing Torpedo
 * Weapon Received: Boomerang Cutter

This is one of the easiest bosses in the game if you have the right weapon. Boomer Kuwanger's main attacks are to throw Boomerang Cutters at you and to try and charge at you. If you get too close, Kuwanger will also grab you with his horns and throw you into the ceiling. Equip the Homing Torpedo and continuously wall jump to defeat him easily; Boomer won't jump and the torpedoes will fly straight at him. If a boomerang is flying your way, dash jump across the room to the other wall.

Sting Chameleon

 * Weakness: Boomerang Cutter
 * Weapon Received: Chameleon Sting

Sting Chameleon is one of the trickier bosses to defeat, mainly because he uses so many different attacks. He will jump across the screen, hit you with his tongue, hang on the wall, throw Chameleon Sting at you, or hang from the ceiling (by his tongue) and make spikes fall from the ceiling. If you hit Sting Chameleon with a Boomerang Cutter, he will immediately stop whatever he's doing and jump to hang from the ceiling by his tongue and drop spikes. He is in a perfect position to be hit by another Boomerang Cutter while hanging, making the battle a simple process of jump, shoot and repeat.

Storm Eagle

 * Weakness: Chameleon Sting
 * Weapon Received: Storm Tornado

Storm Eagle has very few moves that directly attack you; he is more likely to try and shove you off the edge of the platform. He will flap his wings to slightly push you towards the edge or he will fire Storm Tornadoes that do no damage but shove you backwards very forcefully; simply dash towards the middle of the platform to counter these attacks. He will also frequently dive bomb from the top of the screen to the bottom towards you but can easily be avoided by walking or dashing. His last attack involves launching an egg that explodes into four small birds that fly towards you, but they can be destroyed by shooting them. Chameleon Sting makes it easier to hit Storm Eagle, as it fires in three directions, but with careful timing it's just as easy to hit him with regular charged shots.

Flame Mammoth

 * Weakness: Storm Tornado.
 * Weapon Received: Fire Wave.

Flame Mammoth's main attacks are to jump towards you, switch the direction that the conveyor belt moves, and shoot oil and fireballs at you. If a fireball hits an oil puddle it will create a Fire Wave that travels across the screen. To avoid this, use the Boomerang Cutter to cut off his trunk so he can no longer shoot oil puddles. By repeatedly wall jumping to the top of either wall, Flame Mammoth cannot hit you by jumping into you. When hit with Storm Tornado, Flame Mammoth will be momentarily stunned. Keep dodging and shooting and Flame Mammoth is easily beaten.

Bosspider

 * Weakness: Shotgun Ice and X Buster.

The Bosspider can only be damaged when its red eye is open and moves much faster as it takes damage. It will move along a predetermined track as it drops from the ceiling and rushes to the floor. It's only real "attack" is to launch baby spiders which will rush towards you and run up the wall. Shotgun Ice is your best bet since it fires fast and takes little weapon energy to use.

Rangda Bangda

 * Weakness: Chameleon Sting

Rangda Bangda is a boss made up of three parts: two eyes and a nose, however there are three different eyes (colors). Throughout the fight, the walls will close up and the nose will become active. After a short period, the nose will become inactive and the walls will open once again. If two eyes are destroyed, the walls will no longer retract. The best strategy for this fight is to keep all three eyes alive for as long as possible so that you spend less time away from the nose (since the nose moves in a random direction, and you're in a small area, it's easier to be hit). This means you should try and divide the damage you deal between all three colors before destroying them all. Remember, do not destroy the nose first, or the walls will close and you will have to fight the eyes in an enclosed space.

Throughout the fight, one of the eyes will become active (vulnerable) and pop out of the background. Depending on the color, the eye will move towards you (blue), fire shots at you (green), or both (red). When the walls close in, spikes appear underneath them and you must cling to the walls as Rangda Bangda's nose moves between the two walls trying to collide with you. Chameleon Sting does the most damage and using it charged (making you temporarily transparent) can really make the battle easier.

Note that only the moving eyes can be hit with a Hadoken, which only destroys part of the boss (Rangda Bangda can't be beaten in one hit).

D-Rex

 * Weakness: Boomerang Cutter

D-Rex will try to charge you with either its top or bottom half, sometimes one after the other. It can also charge up an energy ball and launch it across the middle of the screen. Boomerang Cutters will do the most damage here. D-Rex can be destroyed by the Hadoken if the bottom section of its body comes at you first. Simply stand on the bottom half and time it correctly to launch the Hadouken as the top half approaches. You'll take the most damage from being hit by its projectiles or being squished in between the lower and upper portions. Taking a hit from being rammed is better than letting the upper portion fall on you.

Velguader

 * Weakness: Shotgun Ice

Sigma's dog bounds across the room and can even use a limited wall jump. It also shoots a fire wave and electric wave towards the ground, which then archs up to the ceiling. Velguader is very fast and is vulnerable to Shotgun Ice.

Sigma

 * Weakness: Electric Spark
 * Weak spot: Body, while moving

Sigma will block your attacks and charge you to attack with his beam saber if you stay on the ground but if you wall jump he will jump diagonally from wall to wall until he is at your level. If you drop, he will jump back down as well, so use this to your advantage. Drop from the wall while firing Electric Spark and he will be unable to block it. Repeat the wall jumping and dropping/firing until he's dead.

Alternatively, if you managed to acquire the Hadouken, keep performing the combination immediately after the two screens of dialogue prior to the fight. If done correctly, you will fire off a Hadouken that will obliterate him immediately.

Wolf Sigma

 * Weakness: Rolling Shield
 * Name note: the name is conjectural and is not named in the credits. Some refer to it as "Sigma 2".

Sigma has four attacks, two from his mouth, and two from each hand: he can breathe fire or shoot electric sparks from his mouth in an arc across the ground, and his hands can either shoot lightning or try and stab you. This will be a long and difficult battle as Sigma doesn't take damage quickly, but you do.

The only way to damage Sigma is to jump on his floating hands when they drop to ground level and ride them up to face level and blast his head with either a fully charged, upgraded X Buster or a Rolling Shield. Rolling Shield will do more damaged than your X Buster, but don't bother charging the weapon because getting too close can be very dangerous. If you can stay on his hands in a safe spot for the duration of the fight, there's no reason for you to take damage.

The spikes you see on Sigma's shoulders in the background cannot damage you, so wall jumping can be utilized to an extent. If you're up in one of the corners, most likely one of the hands will try and charge you. Also note that the electricity sent from the hands can hit you if you're in the corner, so it's definitely not a good place to stay.

Damage Chart
For the Special Weapons, the left number is uncharged shot and right number is charged shot. Also, when using your fully charged pink X-Buster against any boss, you only do 1 damage if you are too close to the enemy.

For X-Buster:
 * 1st number = uncharged shot,
 * 2nd number = 1st charge shot (green),
 * 3rd number = 2nd charge shot (blue),
 * 4th number = 3rd charge shot (arm upgrade)(pink).

The dashing uncharged X-buster always deals 2 damages. The Hadouken always instantly defeats any boss. The only exception is Sigma 2nd form, that cannot be reached by these two attacks.