Mez's Codes...

[Mezmorize]

Paperboy (Europe) [N64]
Regional Lockout Bypass
810C00F4 2400
Note: This allows you to play the PAL game on a NTSC console (JPN/USA).

Another words, bypass this:

[Mezmorize]

Ready 2 Rumble Boxing (Europe) (En,Fr,De) [N64]
Regional Lockout Bypass
80075A80 0014
Note: This allows you to play the PAL game on a NTSC console (JPN/USA).

Another words, bypass this:

[Mezmorize]

RR64 - Ridge Racer 64 (Europe) [N64]
Regional Lockout Bypass
800C6550 0014
800C6040 0014
Note: This allows you to play the PAL game on a NTSC console (JPN/USA).

Another words, bypass this:

[Mezmorize]

Supercross 2000 (Europe) (En,Fr,De) [N64]
Regional Lockout Bypass
800BAAE8 0014
Note: This allows you to play the PAL game on a NTSC console (JPN/USA).

Another words, bypass this:

[Mezmorize]

Tonic Trouble (Europe) (En,Fr,De,Es,It) [N64]
Regional Lockout Bypass
800272BC 0014

Note: This allows you to bypass the region lock screen on a NTSC console (JPN/USA), but you're still stuck at the Ubisoft logo screen.

Another words, bypass this:

[Mezmorize]

Top Gear Hyper-Bike (Europe) [N64]
Regional Lockout Bypass
80032BB4 0014
Note: This allows you to play the PAL game on a NTSC console (JPN/USA).

Another words, bypass this:

[Mezmorize]

WWF Attitude (Europe) [N64]
Regional Lockout Bypass
800A20E4 0014
Note: This allows you to play the PAL game on a NTSC console (JPN/USA).

Another words, bypass this:

[Mezmorize]

Xena - Warrior Princess - The Talisman of Fate (Europe) [N64]
Regional Lockout Bypass
8003C5CC 0014
Note: This allows you to play the PAL game on a NTSC console (JPN/USA).

Another words, bypass this:

[Mezmorize]

40 Winks (Europe) (En,Es,It) (Proto) [N64]
Regional Lockout Bypass
80000258 2400
Note: This allows you to play the PAL game on a NTSC console (JPN/USA).

HSV Adventure Racing! (Australia) [N64]
Regional Lockout Bypass
800006DC 0014
Note: This allows you to play the PAL game on a NTSC console (JPN/USA).

[Mezmorize]

Super Mario Brothers 2 (Japan) (DV 2) [FDS]

Invincible
AEOZLIZZ
Note: You become big Mario when hit as little Mario.

Invincible (alt)
SXOZGSSE
Note: You become big Mario when hit as little Mario.

Enemies & Powerups Can't Move (RAM)
0747:01

Enemies Can't Move
AIUPZIEI

Visually Break Bricks As Small Mario
AEUEEAZA

Jump Through Blocks
AAXZVPPA
Note: You won't be able to get powerups from ? boxes.

Can't Powerup From Little Mario
AANXGKLP

Mushrooms Give Fire Power
TANXGKLP
Note: You'll be a little Mario with fire power though.

Replace Poison Mushrooms With Fire Flowers
PEXAXPGA
Note: If you're little Mario, it'll be a normal mushroom.

Replace Poison Mushrooms With Invincibility Stars
ZEXAXPGA

Replace Poison Mushrooms With 1ups
LEXAXPGA

Invulnerability
ASEXIIEI

Infinite Lives (RAM)
075A:03

Infinite Lives [Can't convert to Game Genie]
701B?CE:AD

127 Lives After Continue
YYEGGZZE
Note: The lives digits will look corrupt.

Super Jump
YISAPAEP
PYSAZEYY

Remove Background Scenery
SZUGLUSE

Music Modifier
D711?00:??
D712?8C:AC
D715?85:84

AAOIPYAE
KZOIZNKE
KAOIIYSA

Theme Song Sounds Remixed (RAM)
07B1:FB

Theme Song Sounds Remixed
UYOIPYAE

[Mezmorize]

Legend of Zelda, The (USA) (Rev A) [NES]

Nevermind, maybe I'll come back to this game later.
Having an issue where the codes I make are not able to be converted to Game Genie, such as this one; and one I had made for using fire over and over in any zone:

Well, it's now later and I figured it out :-)
It seems the game makes a copy of sections of the ROM and puts it into some extended RAM to execute, at least that's my best guess.

Therefore, every single one of the following codes must be enabled before selecting the game file after the Title Screen.

Legend of Zelda, The (USA) (Rev A) [NES]

Infinite Rupee
SZVXASVK

Can Use Candle Ability Over And Over Per Zone
AESZSOET

Infinite Health
OZEULKPX
NYEUGKYE
SAEUIGEN
YTEUTKZE
TAEUYKVG
XTOLAKYV
XTOLPGTE
Note: This code makes you have full 16 hearts upon taking two hits.

Infinite Health
SXVUZUSE

Invulnerability
EYULLLEI
Note: The flames from the blue candle ability can harm you.

Invulnerable To Flames
ENSNKAEI
Note: This is to be able to walk through the flames from the blue candle ability.

Less Enemy Projectiles
SXOLZOVV

Collect Items From Anywhere
AEKZKLLT
AESZELYI

[Mezmorize]

Kirby's Adventure (USA) (Rev A) [NES]

Invulnerability
EYVAYGEI
Note: Enemies die when you touch them.

Invulnerability (Alt)
AASEYEAA
Note: Enemies die when you touch them.

Kirby Turns White After Inhaling Nothing
PEUOOKZE

Inhaled Ability Modifier
B468?00:??
B46A?FD:E3

??=
00-Fire
01-Spark
02-Cutter
03-Sword
04-Fireball
05-Laser
06-Mike
07-Wheel
08-Hammer
09-Parasol
0A-Sleep
0B-Needle
0C-Ice
0D-Freeze
0E-Hi-Jump
0F-Beam
10-Stone
11-Ball
12-Tornado
13-Crash
14-Light
15-Back-Drop
16-Throw
17-U.F.O.
18-Starrod
19-Bye Bye
1A-Normal

Inhaled Ability = Fire
UTVUZKSY

Inhaled Ability = Spark
PAVUAGAA
UTVUZKSY

Inhaled Ability = Cutter
ZAVUAGAA
UTVUZKSY

Inhaled Ability = Sword
LAVUAGAA
UTVUZKSY

Inhaled Ability = Fireball
GAVUAGAA
UTVUZKSY

Inhaled Ability = Laser
IAVUAGAA
UTVUZKSY

Inhaled Ability = Mike
TAVUAGAA
UTVUZKSY

Inhaled Ability = Wheel
YAVUAGAA
UTVUZKSY

Inhaled Ability = Hammer
AAVUAGAE
UTVUZKSY

Inhaled Ability = Parasol
PAVUAGAE
UTVUZKSY

Inhaled Ability = Sleep
ZAVUAGAE
UTVUZKSY

Inhaled Ability = Needle
LAVUAGAE
UTVUZKSY

Inhaled Ability = Ice
GAVUAGAE
UTVUZKSY

Inhaled Ability = Freeze
IAVUAGAE
UTVUZKSY

Inhaled Ability = Hi-Jump
TAVUAGAE
UTVUZKSY

Inhaled Ability = Beam
YAVUAGAE
UTVUZKSY

Inhaled Ability = Stone
APVUAGAA
UTVUZKSY

Inhaled Ability = Ball
PPVUAGAA
UTVUZKSY

Inhaled Ability = Tornado
ZPVUAGAA
UTVUZKSY

Inhaled Ability = Crash
LPVUAGAA
UTVUZKSY

Inhaled Ability = Light
GPVUAGAA
UTVUZKSY

Inhaled Ability = Back-Drop
IPVUAGAA
UTVUZKSY

Inhaled Ability = Throw
TPVUAGAA
UTVUZKSY

Inhaled Ability = U.F.O.
YPVUAGAA
UTVUZKSY

Inhaled Ability = Starrod
APVUAGAE
UTVUZKSY

Inhaled Ability = Bye Bye
PPVUAGAE
UTVUZKSY

Infinite Health
SZEPSVSE

Infinite Lives
SXKTPKVK

Start With 99 Lives
LVVXIYGA

[Mezmorize]

Captain Skyhawk (USA) (Rev A) [NES]

Press Start For 9 Lives
PEEOGLPE
ZEEOTUAG

Press Start For Invulnerability
NNEOGLPE
GEEOTUAK

Press Start For 9 Bombs
PEEOGLPE
POEOTUAG

Press Start For 9 Missiles
PEEOGLPE
ZOEOTUAG

Press Start For 9 Spread Weapon
PEEOGLPE
LOEOTUAG

Press Start To Refill Fuel
EEEOGLPE
GVEOTUAG

Note: Can only have one "Press Start" code on.

Start With 9 Lives
PEUITIIE

Infinite Lives
SZKAIGVG

Infinite Bombs
SZXPUZVG

Infinite Spread Weapon
SXKPVGVG

Infinite Fuel
AAVXYZPA

Invulnerable To Hitting Walls
EYEOZIEI

[Mezmorize]

Operation Wolf (USA) (Rev 0A) [NES]

Take Less Damage
SZOEVLVT

Take No Damage
SZOEVLVT
SXELZZSA

Infinite Bullets
SZSSIISA

Press Start To Reset Damage Bar
PUOKAOUT

Infinite Damage
0031:00

[Mezmorize]

Double Dragon II: The Revenge (USA) (Rev A) [NES]

Press Start To Remove Some Enemies
OXNTVVPK
AENTNTEA
TUNVOTIU

Invulnerability
AEXXOITA

Start With 9 Lives
PASVETGE

Infinite Lives
SUOANXVS

Walk Anywhere On Map
EYUSNZEI

Cheat Mode
AEVOVEIL
Note: Hold Select and press Up or Down to remove nearest enemies. Hold Select and press B to remove all enemies on screen. Hold Select and press A to skip to the next stage.