Mez's Codes...

[Mezmorize]

Here's more untested codes for you to try Unicode:

Megaman II (U) [!]
No Enemies (Some Stages)
EPSNIPEL

No Enemies
ALKSEZAP

No Enemies (Alt)
ALKSUZAP

No Enemies (Alt 2)
EOSPTTEL

More Enemies
ALONGAAP

More Enemies (Alt)
APXYLAAL

Invincible After One Hit
EPUGXTEL

Faster Enemies
EPOKSYEL

Enemies Move Away From You
EOXYAPEL

Enemies Move Away From You (Vertically)
ELKYLZEP

Enemies Move Differently
EOKYLPEL

Enemies Come After You More Aggressivly
EOKNIPEL

Enemies Stop When Far From You
EPSVEYEL

After Jumping, You Fall Down Faster
EPOEUGEL

After Jumping, You Fall Down Slower (And Can Walk In Air)
EPKAEGEL

Enemies Automatically Die
EUSTSTEP

Invulnerability
EIUGVTEY

Invulnerability (Alt)
ESKVETEY

Invulnerability (Alt 2)
ENOVAIEI

Enemies In Some Stages Can't Move
EIVPIZEY

Enemies Fall Straight Down
EIEVVYEY

Walk Backwards
EIUEOPEY

You And Enemies Attack Backwards
EYXTVYEI

Skip READY Dialog At Beginning Of Stage
EYSAIPEI

Invisible
EYKGSTEI

No Sound Effects
EYOALAEI

No Audio
EYXAZAEI

Bubbles Come Out Of Megaman
ENKAOZEI

Stop On The Top Of A Ladder To Fall Down It
APNAVLAL

Hit Anywhere Horizontally
EPXTPTEL

One Bullet Can Kill Multiple Enemies
EINIEZEY

Dropped Items From Enemies Float
ESSUSGEY

Instantly Climb Ladders
ENVATTEI

These were made in the Crashman stage.
I only tried a couple codes in other stages, such as no enemies and noticed it's not for all stages.

[Unicode]

Here's more untested codes for you to try Unicode:

Megaman II (U) [!]
No Enemies (Some Stages)
EPSNIPEL

No Enemies
ALKSEZAP - This codes removes a power-ups placed in levels too.

No Enemies (Alt)
ALKSUZAP - Removes only some enemies, but removes a some power-ups too. Bosses still appears. (Tested on Metal Man's stage.)

No Enemies (Alt 2)
EOSPTTEL

More Enemies
ALONGAAP - Nice

More Enemies (Alt)
APXYLAAL - It removes some enemies from some areas from every stage.

Invincible After One Hit
EPUGXTEL - After while you still can get hit by enemies.

Faster Enemies
EPOKSYEL

Enemies Move Away From You
EOXYAPEL - Doesn't seem to do anything.

Enemies Move Away From You (Vertically)
ELKYLZEP - Useful. Far better than first code.

Enemies Move Differently
EOKYLPEL - Nice

Enemies Come After You More Aggressively
EOKNIPEL - Nice. Makes the game harder.

Enemies Stop When Far From You
EPSVEYEL - This code has a weird glitch - sometimes Mega Buster's shots doesn't travel, and instead stays on one place.

After Jumping, You Fall Down Faster
EPOEUGEL - Useless

After Jumping, You Fall Down Slower (And Can Walk In Air)
EPKAEGEL - Useful. Can't stay on moving platforms normally, though. It should be used with Invincibility to avoid instant death from Laser Beams in Quick Man's stage since you you can't escape from them quickly with this code.

Enemies Automatically Die
EUSTSTEP - Nice, though it doesn't work on all enemies.

Invulnerability
EIUGVTEY - This code already made by @Abystus.

Invulnerability (Alt)
ESKVETEY - You can still take damage from bosses.

Invulnerability (Alt 2)
ENOVAIEI - This make player dies in one hit in boss battles.

Enemies In Some Stages Can't Move
EIVPIZEY

Enemies Fall Straight Down
EIEVVYEY

Walk Backwards
EIUEOPEY

You And Enemies Attack Backwards
EYXTVYEI

Skip READY Dialog At Beginning Of Stage
EYSAIPEI - Useful

Invisible
EYKGSTEI - Useless. You can't climb ladders easy with this code.

No Sound Effects
EYOALAEI - It removes audio completely.

No Audio
EYXAZAEI - Nice

Bubbles Come Out Of Megaman
ENKAOZEI

Stop On The Top Of A Ladder To Fall Down It
APNAVLAL

Hit Anywhere Horizontally
EPXTPTEL - Makes some bosses harder to kill.

One Bullet Can Kill Multiple Enemies
EINIEZEY - Useful

Dropped Items From Enemies Float
ESSUSGEY - Nice

Instantly Climb Ladders
ENVATTEI

These were made in the Crashman stage.
I only tried a couple codes in other stages, such as no enemies and noticed it's not for all stages.

Tested and I got some of these.

[Mezmorize]

Megaman III (U) [!]

No Music
APXEYYAL

No Sound Effects
ELXAZYEP

No Audio
ELEEAPEP

No Audio (Alt)
ENXYKAEI

Slow Decent When Falling
ESVNGYEY

Slow Decent When Falling
APESZAAL
Note: Hold the jump button to fall at regular speed.

Faster Decent When Falling
EPEYNAEL

No Enemies
ALKNEGAP

No Enemies (Alt)
EOOPEGEL

No Enemies (Alt 2)
ELSPVGEP

No Enemies (Alt 3)
ESEPVGEY

Invulnerability (Can't Pick Up Items)
AUNYEZAP

Invulnerability
ESUAGAEY

Invulnerability (Alt)
EISKKIEY

Invulnerability (Alt 2)
ESOEGAEY

Invulnerability (Alt 3)
ESUAGAEY

Some Enemies Can't Move
EOXULGEL

The Longer You Hold Jump, The Higher You Go
EIKGOLEY

The Longer You Hold Jump, The Higher You Go (Alt)
EYUIAAEI

The Longer You Hold Jump, The Higher You Go (Alt 2)
ENUGOTEI

Automatically Grab Ladders After Jumping Under Them
ESEIYGEY

Megaman Is Outlined In White
EYNKAAEI

Instantly Beat Stage?
EYKKVLEI

Start On Last Stage?
EYSGVLEI
Note: Turn the code off to make it stop looping.

Visually Walk Behind Backgrounds
EYOYZYEI

Backgrounds Don't Animate
EYSEYIEI

Hit Anywhere
EOVNNLEL

One Hit Kills
EOKEPPEL

One Hit Kills (Alt)
EIUALZEY

Extra Lives Drop From Enemy Kills
ELNLXYEP

Extra Lives Drop From Enemy Kills (Alt)
ENNYSGEI

Shoot Backwards
ESKETIEY

Automatically Shoot When Jumping
ESSILAEY

Press Up To Climb Walls
ESOILGEY

Press Up To Climb Walls (Alt)
ESOIYGEY

Press Up To Climb Walls (Alt 2)
ESOSIGEY

Can Keep Climbing Ladders After Reaching The Top
ESESZIEY

Can Keep Climbing Ladders After Reaching The Top (Alt)
ESESTIEY

Automatically Climb Ladders
EYOILIEI

Hold B For Rapid-Fire
ENEGUIEI

Kill One Enemy To Beat The Stage
EYSELZEI

Created on Spark Man stage.

[Unicode]

Megaman III (U) [!]

No Music
APXEYYAL

No Sound Effects
ELXAZYEP - It removes only music, but not sounds effects.

No Audio
ELEEAPEP - Nice

No Audio (Alt)
ENXYKAEI - Turning off codes restores only sounds, but for restoring music you have to restart game.

Slow Decent When Falling
ESVNGYEY - Nice

Slow Decent When Falling
APESZAAL
Note: Hold the jump button to fall at regular speed. - Useful

Faster Decent When Falling
EPEYNAEL

No Enemies
ALKNEGAP

No Enemies (Alt)
EOOPEGEL

No Enemies (Alt 2)
ELSPVGEP

No Enemies (Alt 3)
ESEPVGEY - All "No Enemies" codes removes power-ups (Health and Weapon capsules / Extra Lives / Energy tanks) placed into levels, bosses (can't finish stages) and Protoman (you can't even get past places where you need to to fight him to advance).

Invulnerability (Can't Pick Up Items)
AUNYEZAP

Invulnerability
ESUAGAEY - Useful

Invulnerability (Alt)
EISKKIEY - Useful. Best code because it also makes Megaman invincible against spikes.

Invulnerability (Alt 2)
ESOEGAEY - Useful

Invulnerability (Alt 3)
ESUAGAEY - It is the same as "Invulnerability" code.

Some Enemies Can't Move
EOXULGEL - I can't got this code to do anything (tested on Needle Man's and Gemini Man's stages and all enemies stills move).

The Longer You Hold Jump, The Higher You Go
EIKGOLEY - Nice

The Longer You Hold Jump, The Higher You Go (Alt)
EYUIAAEI - Useful. It gives you slower falling after jumping.

The Longer You Hold Jump, The Higher You Go (Alt 2)
ENUGOTEI - Nice

Automatically Grab Ladders After Jumping Under Them
ESEIYGEY - Doesn't let Megaman to climb ladders down.

Megaman Is Outlined In White
EYNKAAEI - Doesn't change Mega Man's sprite look, but messes up intro and stage select screen.

Instantly Beat Stage?
EYKKVLEI

Start On Last Stage?
EYSGVLEI
Note: Turn the code off to make it stop looping. - Nice

Visually Walk Behind Backgrounds
EYOYZYEI - Nice

Backgrounds Don't Animate
EYSEYIEI - Nice

Hit Anywhere
EOVNNLEL - Useful

One Hit Kills
EOKEPPEL - Useful

One Hit Kills (Alt)
EIUALZEY - Doesn't work on bosses (tested on Needle Man's stage boss).

Extra Lives Drop From Enemy Kills
ELNLXYEP - Useful

Extra Lives Drop From Enemy Kills (Alt)
ENNYSGEI - Useful

Shoot Backwards
ESKETIEY

Automatically Shoot When Jumping
ESSILAEY - Nice

Press Up To Climb Walls
ESOILGEY

Press Up To Climb Walls (Alt)
ESOIYGEY

Press Up To Climb Walls (Alt 2)
ESOSIGEY - All three "Press Up To Climb Walls" doesn't let to press Down + A to make Mega Man to slide, which might be problem on narrow passages where you need exactly sliding to pass these areas.

Can Keep Climbing Ladders After Reaching The Top
ESESZIEY

Can Keep Climbing Ladders After Reaching The Top (Alt)
ESESTIEY

Automatically Climb Ladders
EYOILIEI

Hold B For Rapid-Fire
ENEGUIEI - Useful

Kill One Enemy To Beat The Stage
EYSELZEI - Totally bad. I got stuck on Sparkman's Doc stage.

Created on Spark Man stage.

I didn't have time to test all codes. Will continue testing later.

[Mezmorize]

Thanks for all the testing Unicode.
Here's codes for Megaman 4, created on Ring Man stage, only went to another stage to test out invincibility on spikes.
Enemies are the cannons, and 'color beams' are the things you see at the beginning of Ring Man stage.

Megaman IV (U) (PRG0) [!]
No Music
APXEYYAL

No Music (Alt)
ESOEILEY

No Sound Effects
ELXAZYEP

No Sound Effects (Alt)
EISAGZEY

No Audio
ESUEGIEY

No Audio (Alt)
EYSNVYEI

Hyper Speed Music
AUVEALAP

Backgrounds Change Colors
AOOLOAAL

Foregrounds Change Colors
ALOUEAAP

Color Beams Are Harder To Walk Across
AOSXLAAL

Color Beams Are Easier To Walk Across
EOONOPEL

Color Beams Do Not Move When Standing On Them
ALXXTAAP

Color Beams Do Not Move When Standing On Them (Alt)
EOXNUPEL

Color Beams Do Not Move When Standing On Them (Alt 2)
EPXZYAEL

Color Beams Do Not Move When Standing On Them (Alt 3)
EIOZAPEY

Color Beams Do Not Move When Standing On Them (Alt 4)
ENEYOPEI

Color Beams Move When Not Standing On Them
EPOXTAEL

Invulnerability
AUUAIPAP
Note: Spikes still kill you.

Invulnerability (Alt)
ENUEPPEI
Note: Spikes still kill you.

Invulnerability
ESSAPAEY

Enemies Shoot In The Opposite Direction
EPXNAYEL

Enemies Shoot Backwards
EPUNYYEL

Enemies Don't Shoot In Some Angles
EPVYAYEL

Enemies Don't Shoot In Some Angles (Alt)
EPVYYYEL

Enemies Shoot Differently
EOUNTYEL

Fall Down Faster
EPOYYLEL

Enemies Don't Shoot
EPUOEAEL

Enemies Don't Shoot (Alt)
EIXOOAEY

Enemies Don't Shoot (Alt 2)
EYNYVLEI

Stage Backgrounds Are Dark
EIXVGGEY

Can Keep Climbing Ladders After Reaching The Top
ESNIGGEY

Can Keep Climbing Ladders After Reaching The Top (Alt)
ENKIGGEI

Can Keep Climbing Ladders After Reaching The Top (Alt 2)
APSETGAL

Automatically Shoot
EIUAUIEY
Note: Turn off to climb ladders.

Automatically Shoot
EUNAKGEP

Automatically Grab Ladders
EIXOYZEY

Enemy Shots Travel Horizontally
EIUNPGEY

Enemies Can't Shoot Downward
EIUNIGEY

Slow Motion
ENNKTAEI

Walk Behind Backgrounds
ENNGYTEI

Enemies Only Shoot Up
ENXPNAEI

Enemies Only Shoot Down
ENUOEAEI

The Longer You Hold Jump, The Higher You Go
EYSNAPEI

Enemies Shoots Less Bullets
ENEPOAEI

Hit Almost Anywhere
EOXNSZEL

One Hit Kills
EPUALLEL

Shoot A Normal And Charged Shot At The Same Time
EUOAGAEP

Shoot Backwards
ESEESIEY

One Shot Can Kill Multiple Enemies
ESUEIZEY

One Shot Can Kill Multiple Enemies (And Takes Less Shots)
ESNAGZEY

Takes Less Shots To Kill Enemies
ESNEAZEY

Takes Less Shots To Kill Enemies (Alt)
ENNEGZEI

--------------------------------------------------------------------
Megaman V (U) [!]
Created on Stone Man stage:

No Music
APXEYYAL

Hyper Music
AUVEALAP

No Sound Effects
ALXAZYEP

No Sound Effects (Alt)
ELUAIPEP

Mostly No Audio
ELEEAPEP

Backgrounds Change Colors
AUEINLAP

You And Enemies Fall Faster
EOSTKPEL

Fall Faster
EUSVTYEP

Auto Shoot
ELXPGPEP

Auto Shoot (Alt)
ESVPYAEY

Stages Are Colored Differently, With No Enemies
EUVPEAEP

Slow Motion
EISGZYEY

No Walking Animation
ESEELPEY

Invulnerability (Can't Pick Up Items)
AUEVUYAP

Invulnerability (But Can't Kill Most Enemies)
ESNVAAEY

Invulnerability
ASEAIAAP
Note: Spikes still kill you.

Invulnerability (Alt)
ESKATZEY
Note: Spikes still kill you.

Invulnerability (Alt 2)
ENEEZAEI
Note: Spikes still kill you.

Invulnerability (Alt 3)
ENKEGZEI
Note: Spikes still kill you.

Debug Mode Showing
EIXSVYEY

After Jumping, You Stay In The Air
EYXTVAEI
Note: To fall back down, turn off the code.

The Longer You Hold Jump, The Higher You Go
ANVOPTEI

Automatically Charge Up For Stronger Shots
EYOOTPEI

No Enemies
ENOONAEI

No Enemies (Alt)
EPOPOPEL

No Enemies (Alt 2)
EOXPVPEL

No Enemies (Alt 3)
EUVOOAEP

Hyper Character/Enemy Animations
ENSVAAEI

Enemies Don't Pop Out Of The Ground
EOXTUGEL

Enemies Don't Pop Out Of The Ground (Alt)
EPNVSGEL

Enemies Automatically Die As You Aproach
EPNATAEL
Note: An annoying sound effect will often play though.

Hit Almost Anywhere
EPKNTAEL

Enemies That Pop Out Of The Ground Shoot 2 Bullets Instead Of 3
EPSVSPEL

Enemies That Pop Out Of The Ground Don't Shoot
EPNXYPEL

Enemies That Pop Out Of The Ground Don't Turn Into 3 Smaller Enemies When Shot
EPEXIPEL

Enemies That Pop Out Of The Ground Don't Turn Into 3 Smaller Enemies When Shot (Alt)
ENXZYPEI

Enemies That Pop Out Of The Ground Shoot Away From You
ELXVEGEP

Enemies That Pop Out Of The Ground's 3 Miniture Versions Don't Move Horizontally
EUUXYPEP

Enemies That Pop Out Of The Ground's 3 Miniture Versions Don't Move Horizontally (Alt)
ESUXAPEY

Normal Shots Are Charged, Charged Shots Are Normal
EUKOZPEP

Enemies Drop Large Blue Bars
EUEZVTEP

Enemies Drop Large Blue Bars (Alt)
EYOYPZEI

Reverse The Function Of The Left And Right Buttons
EIKVOZEY

Shoot Backwards
ESUOTPEY

You And Enemies Shoot Backwards
EIVVVZEY

Backgrounds Flash After You Recieve Damage
EIETZPEY

One Shot Can Kill Multiple Enemies
ESVATPEY

One Shot Can Kill Multiple Enemies (Alt)
ESVEZPEY

After Killing An Enemy, Your Bullet Travels Diagonally
ESNAPPEY

Your Bullets Travel Lower And Faster
EYOOAZEI

Shoot Once, And A Charged Shot Follows
EYKOTPEI

Get Knocked Forwards Instead Of Backwards From Taking Damage
ENOATGEI

[Unicode]

Thanks for all the testing Unicode.
Here's codes for Megaman 4, created on Ring Man stage, only went to another stage to test out invincibility on spikes.
Enemies are the cannons, and 'color beams' are the things you see at the beginning of Ring Man stage.

Megaman IV (U) (PRG0) [!]
No Music
APXEYYAL - Nice

No Music (Alt)
ESOEILEY - If I activate this code while game is playing, music starts to sound frozen.

No Sound Effects
ELXAZYEP - Nice

No Sound Effects (Alt)
EISAGZEY - Nice

No Audio
ESUEGIEY - Doesn't disable music completely.

No Audio (Alt)
EYSNVYEI - Make music looping, but it stills plays.

Hyper Speed Music
AUVEALAP - Nice

Backgrounds Change Colors
AOOLOAAL

Foregrounds Change Colors
ALOUEAAP

Color Beams Are Harder To Walk Across
AOSXLAAL

Color Beams Are Easier To Walk Across
EOONOPEL

Color Beams Do Not Move When Standing On Them
ALXXTAAP

Color Beams Do Not Move When Standing On Them (Alt)
EOXNUPEL

Color Beams Do Not Move When Standing On Them (Alt 2)
EPXZYAEL

Color Beams Do Not Move When Standing On Them (Alt 3)
EIOZAPEY

Color Beams Do Not Move When Standing On Them (Alt 4)
ENEYOPEI

Color Beams Move When Not Standing On Them
EPOXTAEL

Invulnerability
AUUAIPAP
Note: Spikes still kill you. - Useful

Invulnerability (Alt)
ENUEPPEI
Note: Spikes still kill you. - Useful

Invulnerability
ESSAPAEY - Useful

Enemies Shoot In The Opposite Direction
EPXNAYEL

Enemies Shoot Backwards
EPUNYYEL

Enemies Don't Shoot In Some Angles
EPVYAYEL

Enemies Don't Shoot In Some Angles (Alt)
EPVYYYEL

Enemies Shoot Differently
EOUNTYEL - I can't get any of these codes working (tested on Drill Man's and Bright Man's stages)

Fall Down Faster
EPOYYLEL

Enemies Don't Shoot
EPUOEAEL

Enemies Don't Shoot (Alt)
EIXOOAEY - These two does nothing. On both versions of the game PRG0 and PRG1 enemies stills can shoot.

Enemies Don't Shoot (Alt 2)
EYNYVLEI - Useful. It's the only one I got working.

Stage Backgrounds Are Dark
EIXVGGEY - Nice, though it makes game harder for playing.

Can Keep Climbing Ladders After Reaching The Top
ESNIGGEY

Can Keep Climbing Ladders After Reaching The Top (Alt)
ENKIGGEI

Can Keep Climbing Ladders After Reaching The Top (Alt 2)
APSETGAL

Automatically Shoot
EIUAUIEY
Note: Turn off to climb ladders. - Useful

Automatically Shoot
EUNAKGEP - Doesn't let to climb ladders.

Automatically Grab Ladders
EIXOYZEY

Enemy Shots Travel Horizontally
EIUNPGEY

Enemies Can't Shoot Downward
EIUNIGEY

Slow Motion
ENNKTAEI - Useful

Walk Behind Backgrounds
ENNGYTEI - Nice

Enemies Only Shoot Up
ENXPNAEI

Enemies Only Shoot Down
ENUOEAEI

The Longer You Hold Jump, The Higher You Go
EYSNAPEI - Useful

Enemies Shoots Less Bullets
ENEPOAEI

Hit Almost Anywhere
EOXNSZEL - Useful

One Hit Kills
EPUALLEL - Useful

Shoot A Normal And Charged Shot At The Same Time
EUOAGAEP - Useful

Shoot Backwards
ESEESIEY

One Shot Can Kill Multiple Enemies
ESUEIZEY - You can't kill some enemies with this.

One Shot Can Kill Multiple Enemies (And Takes Less Shots)
ESNAGZEY - Useful


Takes Less Shots To Kill Enemies
ESNEAZEY - Firing a full charget Megabuster shot takes a less damage to bosses (Tested on Bright Man)

Takes Less Shots To Kill Enemies (Alt)
ENNEGZEI - Useful

--------------------------------------------------------------------
Megaman V (U) [!]
Created on Stone Man stage:

No Music
APXEYYAL - Nice

Hyper Music
AUVEALAP

No Sound Effects
ALXAZYEP - Not working at all.

No Sound Effects (Alt)
ELUAIPEP - Nice

Mostly No Audio
ELEEAPEP - This code actually disables audio completely.

Backgrounds Change Colors
AUEINLAP

You And Enemies Fall Faster
EOSTKPEL

Fall Faster
EUSVTYEP

Auto Shoot
ELXPGPEP - Can't climb ladders.

Auto Shoot (Alt)
ESVPYAEY - Useless

Stages Are Colored Differently, With No Enemies
EUVPEAEP - Useless

Slow Motion
EISGZYEY - Useful

No Walking Animation
ESEELPEY - Nice

Invulnerability (Can't Pick Up Items)
AUEVUYAP

Invulnerability (But Can't Kill Most Enemies)
ESNVAAEY - Useless

Invulnerability
ASEAIAAP
Note: Spikes still kill you. - Doesn't let to use some platforms - you take damage from them and you'll fall into pits.

Invulnerability (Alt)
ESKATZEY
Note: Spikes still kill you. - Useful

Invulnerability (Alt 2)
ENEEZAEI
Note: Spikes still kill you. - Useful

Invulnerability (Alt 3)
ENKEGZEI
Note: Spikes still kill you. - Useful

Debug Mode Showing
EIXSVYEY

After Jumping, You Stay In The Air
EYXTVAEI
Note: To fall back down, turn off the code. - Applies for enemies and bosses too.

The Longer You Hold Jump, The Higher You Go
ANVOPTEI - Useful

Automatically Charge Up For Stronger Shots
EYOOTPEI - Useful

No Enemies
ENOONAEI

No Enemies (Alt)
EPOPOPEL

No Enemies (Alt 2)
EOXPVPEL

No Enemies (Alt 3)
EUVOOAEP

Hyper Character/Enemy Animations
ENSVAAEI - Bad code.

Enemies Don't Pop Out Of The Ground
EOXTUGEL

Enemies Don't Pop Out Of The Ground (Alt)
EPNVSGEL

Enemies Automatically Die As You Aproach
EPNATAEL
Note: An annoying sound effect will often play though. - Useful

Hit Almost Anywhere
EPKNTAEL - Doesn't work well.

Enemies That Pop Out Of The Ground Shoot 2 Bullets Instead Of 3
EPSVSPEL

Enemies That Pop Out Of The Ground Don't Shoot
EPNXYPEL

Enemies That Pop Out Of The Ground Don't Turn Into 3 Smaller Enemies When Shot
EPEXIPEL

Enemies That Pop Out Of The Ground Don't Turn Into 3 Smaller Enemies When Shot (Alt)
ENXZYPEI

Enemies That Pop Out Of The Ground Shoot Away From You
ELXVEGEP

Enemies That Pop Out Of The Ground's 3 Miniture Versions Don't Move Horizontally
EUUXYPEP

Enemies That Pop Out Of The Ground's 3 Miniture Versions Don't Move Horizontally (Alt)
ESUXAPEY

Normal Shots Are Charged, Charged Shots Are Normal
EUKOZPEP

Enemies Drop Large Blue Bars
EUEZVTEP

Enemies Drop Large Blue Bars (Alt)
EYOYPZEI

Reverse The Function Of The Left And Right Buttons
EIKVOZEY - Useless

Shoot Backwards
ESUOTPEY

You And Enemies Shoot Backwards
EIVVVZEY

Backgrounds Flash After You Receive Damage
EIETZPEY - It also flashes when you shoot an enemy.

One Shot Can Kill Multiple Enemies
ESVATPEY - Useful

One Shot Can Kill Multiple Enemies (Alt)
ESVEZPEY - Useful

After Killing An Enemy, Your Bullet Travels Diagonally
ESNAPPEY

Your Bullets Travel Lower And Faster
EYOOAZEI - Nice

Shoot Once, And A Charged Shot Follows
EYKOTPEI - Useful

Get Knocked Forwards Instead Of Backwards From Taking Damage
ENOATGEI

Tested and added proper codes.

[Mezmorize]

Thanks for all the testing Unicode.
Here's codes for Megaman 4, created on Ring Man stage, only went to another stage to test out invincibility on spikes.
Enemies are the cannons, and 'color beams' are the things you see at the beginning of Ring Man stage.

Megaman IV (U) (PRG0) [!]

Enemies Shoot In The Opposite Direction
EPXNAYEL

Enemies Shoot Backwards
EPUNYYEL

Enemies Don't Shoot In Some Angles
EPVYAYEL

Enemies Don't Shoot In Some Angles (Alt)
EPVYYYEL

Enemies Shoot Differently
EOUNTYEL

Since these do work for the cannon enemies on Ring Man stage, you could just rename the code.

Color Beams Do Not Move When Standing On Them
ALXXTAAP

Color Beams Do Not Move When Standing On Them (Alt)
EOXNUPEL

Color Beams Do Not Move When Standing On Them (Alt 2)
EPXZYAEL

Color Beams Do Not Move When Standing On Them (Alt 3)
EIOZAPEY

Color Beams Do Not Move When Standing On Them (Alt 4)
ENEYOPEI

I'm curious to why you tagged these as useless, they make the Ring Man stage much easier since you don't have to worry about falling thru them.

[Mezmorize]

Finished with your request for the Megaman series, Castlevania will be next.

The following are for Megaman VI (U) [!] and were created on Blizzard Man stage.

No Music
APXETYAL

No Sound Effects
ELXAPYEP

No Sound Effects (Alt)
EINAIAEY

No Audio
ELEEAPEP

Fight The Stage Boss
ELKAYPEP
Note: Turn the code on after the stage has loaded.

Warp To The Last Stage
EIVGSIEY
Note: Turn the code off to stop it from looping.

Automatically Shoot
ELKAATEP

Invulnerability
EUKEOTEP
Note: Can't stand on the timer bombs or pick up items.

Invulnerability
ESXAKTEY

Invulnerability (Alt)
EYNAKYEI

Invulnerability (Alt 2)
EYNEEYEI

Randomly Shoot Charged Shots
ANXAZTEP

No Enemies Or Powerups
EIUETPEY

No Enemies Or Powerups (Alt)
EOKAYPEL

Stage Colors Change After Shooting Once
ESNVOLEY

Auto Shoot When Standing
EYUKGYEI

Automatically Shoot
EYUAATEI

Don't Slide On Ice
AIOANLEI

Auto Charge Up Shots
EYUATTEI

The Longer You Hold Jump, The Higher You Go
ENSEGTEI

Megaman Changes To Red After Shooting Once
EYNAATEI

Walrus Enemies Face Away From You
AOKVAIAL

Walrus Enemies Can't Shoot
AOSPEGAL

One Hit Kills Walrus Enemies
ALOVKLAP

One Hit Kills
EOEPIAEL

No Walrus Enemies
EOKTOZEL

Enemies Can't Shoot Some Projectiles
EPNTKZEL

Enemies Can't Shoot
EOXVTIEL

Enemies Can't Shoot (Alt)
EYEVXTEI

Enemies Drop Large Health Spheres
ELVGKGEP

Don't Get Knocked Back From Taking Damage
EYOEAIEI

Increased Drop Rate Upon Enemy Death
ENNAGPEI

[Unicode]

Finished with your request for the Megaman series, Castlevania will be next.

The following are for Megaman VI (U) [!] and were created on Blizzard Man stage.

No Music
APXETYAL - Nice

No Sound Effects
ELXAPYEP - Nice

No Sound Effects (Alt)
EINAIAEY

No Audio
ELEEAPEP - Music stills play when you're not shooting.

Fight The Stage Boss
ELKAYPEP
Note: Turn the code on after the stage has loaded. - Nice

Warp To The Last Stage
EIVGSIEY
Note: Turn the code off to stop it from looping. - But it make start without any weapons or rush.

Automatically Shoot
ELKAATEP - Can't climb ladders with this code

Invulnerability
EUKEOTEP
Note: Can't stand on the timer bombs or pick up items.

Invulnerability
ESXAKTEY - Already made by @Abystus.

Invulnerability (Alt)
EYNAKYEI - Useful

Invulnerability (Alt 2)
EYNEEYEI - Useful

Randomly Shoot Charged Shots
ANXAZTEP - Nice

No Enemies Or Powerups
EIUETPEY

No Enemies Or Powerups (Alt)
EOKAYPEL

Stage Colors Change After Shooting Once
ESNVOLEY

Auto Shoot When Standing
EYUKGYEI - Useless. Makes shooting enemies more difficult.

Automatically Shoot
EYUAATEI - Cannot climb ladders with this code.

Don't Slide On Ice
AIOANLEI - Useful

Auto Charge Up Shots
EYUATTEI - Useful

The Longer You Hold Jump, The Higher You Go
ENSEGTEI - Can't jump higher underwater (tested on Centaur Man's stage).

Megaman Changes To Red After Shooting Once
EYNAATEI

Walrus Enemies Face Away From You
AOKVAIAL - This applies for other enemies and bosses too. It actually makes fights with bosses easier. Please rename the code name to "Enemies Face Away From You".

Walrus Enemies Can't Shoot
AOSPEGAL - Useful

One Hit Kills Walrus Enemies
ALOVKLAP

One Hit Kills
EOEPIAEL - Doesn't work on bosses and some enemies (tested on Wind Man).

No Walrus Enemies
EOKTOZEL - It removes some other enemies too.

Enemies Can't Shoot Some Projectiles
EPNTKZEL - Useful
Enemies Can't Shoot
EOXVTIEL - This code makes the machines dropping Metools in Tomahawk Man's stage look glitchly after being destroyed. Also disables items (Health / Weapons capsules, Extra Lives, E-Tanks) dropped by Eddie too.

Enemies Can't Shoot (Alt)
EYEVXTEI - No effect - enemies still can shoot.

Enemies Drop Large Health Spheres
ELVGKGEP

Don't Get Knocked Back From Taking Damage
EYOEAIEI

Increased Drop Rate Upon Enemy Death
ENNAGPEI

Thanks. I added proper codes for Mega Man 6 and "Rainbow beam" type codes for Mega Man 4 noted by you early.

Only one warning about Castlevania games: the first Castlevania game have a two versions - PRG0 and PRG1, as a code working on the one version of the game probably won't work on the other.

[Mezmorize]

If you will, try some of the problematic codes with a different value used:
----------------------------------------
Hudson's Adventure Island (U) [!]
Powerups Are Worth More Points
ANXEKLEY
ESXEKLEY - This reduces points you get from fruits in bonus stages. It stills good though.

Points Continue Rising From Powerups Until You Move
AIOAOLEY
EIOAOLEY - Some fruits seems are noncollectable with this code.

Touching Obsticles And Enemies Kills Them
AYVGPAEY
EIVGPAEY - You must avoid touching every boss on end of every area #-4 or the game will not continue.
Also, it makes you to have a Fairy Bee invincibility, however, having a real Fairy Bee from an egg makes the player vulnerable to enemies.

-----------------------------------------
Hudson's Adventure Island II (U) [!]
Get 2,000 Points At Start Of Round
ANVXOZEP
EUVXOZEP - This works only if you doesn't have a dinosaur riding in beginning of the stage.

Automatically Run, Hold B To Walk
ANEZYAEY
ESEZYAEY - This works only if you doesn't have a dinosaur riding.

Hold Jump To Slowly Float, Let Go To Slowly Fall
AYOLIPEI
EYOLIPEI - Pterodactyl (the flying dinosaur) cannot fly with this code.

Invulnerability
ASXSUTEL
EOXSUTEL - You will die if try to collect a key for Island Skip Room / Secret Room / Bonus stages from an hidden egg.

-----------------------------------------
Hudson's Adventure Island III (U) [!]
Swim In The Air
ANEZPYEI
ENEZPYEI - You'll lose any dinosaur (except the purple swimming one) when using the code.

Touching Enemies Kills Them
AYKZNGEY
EIKZNGEY - Running into enemies while having an Invincibility bee will kill the player.

Touching Enemies Kills Them (Alt)
ANXZOGEY
ESXZOGEY - Touching an enemy while having a dinosaur causes an instant death.

-----------------
Megaman IV (U) (PRG0) [!]
Takes Less Shots To Kill Enemies
ASNEAZEY
ESNEAZEY - Firing a full charget Megabuster shot takes a less damage to bosses (Tested on Bright Man)

-------------------------------------------------------------------
Megaman VI (U) [!]
The Longer You Hold Jump, The Higher You Go
ANSEGTEI
ENSEGTEI - Can't jump higher underwater (tested on Centaur Man's stage).

[seznam88]

you can create invincibility code for out of this world for SNES
thank you

[Unicode]

If you will, try some of the problematic codes with a different value used:
----------------------------------------
Hudson's Adventure Island (U) [!]
Powerups Are Worth More Points
ANXEKLEY
ESXEKLEY - This reduces points you get from fruits in bonus stages. It stills good though. - This code works properly. It gives a 500 pts. from all fruits on normal stages, as on bonus area you stills get 500 points from each fruit there (default amount).

Points Continue Rising From Powerups Until You Move
AIOAOLEY
EIOAOLEY - Some fruits seems are noncollectable with this code. - Some tiny gliches with score display from collected food, but still far better than old code.

Touching Obsticles And Enemies Kills Them
AYVGPAEY
EIVGPAEY - You must avoid touching every boss on end of every area #-4 or the game will not continue.
Also, it makes you to have a Fairy Bee invincibility, however, having a real Fairy Bee from an egg makes the player vulnerable to enemies. - Still same issue.

-----------------------------------------
Hudson's Adventure Island II (U) [!]
Get 2,000 Points At Start Of Round
ANVXOZEP
EUVXOZEP - This works only if you doesn't have a dinosaur riding in beginning of the stage. - You still doesn't get 2000 points if you're riding a dinosaur at beginning of the stage.

Automatically Run, Hold B To Walk
ANEZYAEY
ESEZYAEY - This works only if you doesn't have a dinosaur riding. - Still doesn't works with dinosaurs.

Hold Jump To Slowly Float, Let Go To Slowly Fall
AYOLIPEI
EYOLIPEI - Pterodactyl (the flying dinosaur) cannot fly with this code. - This code doesn't have the issues with Pterodactyl and you can fly with it, unlike previous version.

Invulnerability
ASXSUTEL
EOXSUTEL - You will die if try to collect a key for Island Skip Room / Secret Room / Bonus stages from an hidden egg. - Alternative version is bad too - it make player dies when touching any eggs..

-----------------------------------------
Hudson's Adventure Island III (U) [!]
Swim In The Air
ANEZPYEI
ENEZPYEI - You'll lose any dinosaur (except the purple swimming one) when using the code. - Same with alternative code.

Touching Enemies Kills Them
AYKZNGEY
EIKZNGEY - Running into enemies while having an Invincibility bee will kill the player. - Same issues as the other code below, except this dinosaur isn't lost when touch a star-like spikes located on the sea.

Touching Enemies Kills Them (Alt)
ANXZOGEY
ESXZOGEY - Touching an enemy while having a dinosaur causes an instant death. - I tested this code on World 4's boss and it disables boss from appearing and also make dinosaur disappears when touch any of these static and moving star-like spikes in water.

-----------------
Megaman IV (U) (PRG0) [!]
Takes Less Shots To Kill Enemies
ASNEAZEY
ESNEAZEY - Firing a full charged Megabuster shot takes a less damage to bosses (Tested on Bright Man) - This a good as it doesn't have the bug from the older code.

-------------------------------------------------------------------
Megaman VI (U) [!]
The Longer You Hold Jump, The Higher You Go
ANSEGTEI
ENSEGTEI - Can't jump higher underwater (tested on Centaur Man's stage). - Little better than old code.

I added only following codes:

Hudson's Adventure Island (U):
Powerups Are Worth More Points ANXEKLEY;
Points Continue Rising From Powerups Until You Move AIOAOLEY;

Hudson's Adventure Island II (U):
Hold Jump To Slowly Float, Let Go To Slowly Fall AYOLIPEI

Both codes for Mega Man 4 and 6.

All other codes has an errors.

[Mezmorize]

Castlevania (U) (PRG1) [!]

No Music
AOOEZZAL

No Audio
ELOEIZEP

Some Audio Notes Are Louder
EYVEZIEI

No Enemies Or Items
APXTNPAL

No Enemies Or Items (Alt)
EPXVVPEL

No Enemies
EUEYALEP

No Enemies (Alt)
EYNNLLEI

Invincibility
APSTTYAL

Invulnerability
ESSTGTEY

Invulnerability
ESKTATEY
Note: Can't pick up items.

Invulnerability (Alt)
EOEVKYEL
Note: Can't pick up items.

Invulnerability
AOSVTGAL
Note: Can't kill enemies or get items.

Invulnerability (Alt)
ELETAIEP
Note: Can't kill enemies or get items.

Invulnerability (Blinking)
ESNTXAEY

Whip Is Invisible
APSZZGAL

Whip Is Invisible (Alt)
EUXXGLEP

Hit Almost Anywhere
EPUVTIEL

Fall Faster
EOSPZGEL

Fall Faster (Alt)
EOSPYGEL

Enemies Don't Move
EIUTVPEY

Some Enemies Die As You Approach
EIEVGIEY

Infinite Time
ESUZLZEY

Infinite Time (Alt)
ENXZYAEI

Attack Crouched Down
ESXOKZEY

Walk Out Of The Ground At Beginning Of Stage
ENSKAZEI

Slower Walking
EYSXKIEI

Enemies Count As Hearts
ANKVITEI

Everything Counts As Hearts, Including Enemies
AIOTTYEI

Hearts And Other Things Are Gold Instead Of Red
EYEALPEI

Screen Scrolls With You At The Far Left Instead Of Center
ENXPXAEI

Enemies Die Before Your Whip Actually Touches Them
EYEVLGEI

Enemies Coming From The Right Move Faster
EPSVETEL

Enemies Disappear
EPETOZEL

Less Enemies
EOONYLEL

Less Enemies (Alt)
EUONLLEP

Enemies Cause More Damage
EPKVAYEL

Don't Get Knocked Back From Taking Damage
EUSPGTEP

Don't Get Knocked Back From Taking Damage (Alt)
ENKPTTEI

Hidden Items Appear?
EUKXOAEP
Note: When you use the whip at the very start of the first stage (in the castle) an item will drop from the second glass window.

Killing Enemies Grants Extra Lives
ELOKOLEP

Enemies Run Away From You Instead Of Towards
EIKVUTEY

Some Enemies Can't Move
EIOETAEY

Bats Are In First Part Of Castle
ESVAIAEY

Recieving Damage Grants Points
EIOVIYEY

Increased Drops?
ESUTIAEY

Drops Don't Fall To The Ground
ESKSXIEY

All Items Clears The Screen Of Enemies
ESEVGYEY

All Items Makes You Pass Thru Enemies
ESOTAYEY

Some Enemies Fall Thru The Floor
EYEELAEI

Some Enemies Travel Slower
EYXEAAEI

Some Enemies Are Gold Color
EYSEGPEI

When An Enemy Touches You, They Travel The Opposite Direction
EYXVPYEI

[OldSchoolGamer]

What's the difference between Invulnerability and Invincibility?

Infinite Energy/Health you can still get hit, but it takes away no damage from you

Invincibility you cannot get hit, you walk through enemies and vice versa.

So what's Invulnerability?

[Mezmorize]

Well going by an English dictionary, invincibility means Incapable of being defeated (infinite health).
Invulnerability's definition is Immune to attack; Impossible to damage (walk thru enemies).