Here are some codes which you should try out!!

For many games, NOTINE, PINEAP, and KILLIT do cool things.

DuckTales
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NTLLVT = Weird
STLLVT = 1-ups from treasure
KTLLVT = Invincibility from treasure
UTLLVT = Cakes from treasure
XTLLVT = Ice cream cones from treasure
OTLLVT = Small diamonds from treasure
ETLLVT = Large diamonds from treasure

Gyruss
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NYTATG = "Unwrapped" levels
NYTAYG = Pause, change gfx. with buttons
NPSEGA = Strobe, stretched
KZSEGA = Small stars
VZSEGA = Strobe 2
VLSEGA = Weird

Little Nemo
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OEUKOZAA = Level 2 with morning star
UEUKOZAA =   "   4   "    "      "
KEUKOZAA =   "   6   "    "      "
PXUKOZAA = End boss music
GUUKOZAA = Level 4 music
OKUKOZAA = Intro music
ZUUKOZAA = Title music
SXUKOZAA = Level 6 music
TXUKOZAA = Weird level
YXUKOZAA = Really weird
USUKOZAA = Level 1 music
KUUKOZAA = Level 3 music
GNUKOZAA = Weird music
AEUKOZAE = Later in Nightmare Land

MegaMan
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EATINE = Weird

MegaMan V
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AANEAP = Kill all enemies
SIIIII = Weird colours

Super Mario Bros. 3
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SUKXGLIE = "Swimming" Mario
SIIIII   = Cool stuff
NNIGAV   = Characters gone
NNPGAV   = Go under pipes
NNZGAV   = Weird
