CASTLEVANIA Aria of Sorrow
Ending 1:
Simply beat the new heir to Dracula.
Ending 2:
Have the Succubus, Giant Bat, and Flame Demon souls equipped to get another side quest after you beat Graham.

CASTLEVANIA: Harmony of Dissonance

Ending 1:
Simply beat the game in the A type Castle by finishing off Maxim.
Ending 2:
Find all of Dracula's 6 body parts and kill Maxim in the B type Castle.
Ending 3:
Have all of Dracula's parts but before you enter the final chamber have the MK and JB braclets equiped.
Secret Codes:
If you're main title screen turns red then you can enter these codes:
MAXIM -play as the sword weilding hero.
NO MAGIC -play the game with no spell books.
HARDGAME -Juste's game is now more challenging of course.

Power up:
Pause the game and Press Up, Up, Down, Down, L, R, L, R, B, A then unpause.
Power up Fake code:
Pause the game and Press Up, Up, Down, Down, Left, Right, Left, Right, B, A then unpause. You'll get the power ups but not for very long.

METROID II Return of Samus
Alternate endings:
Finish the game in under 3hours to see Samus in a biniki.
Finish the game in under 5hours to see Samus with her helmet off.
Finish the game in over 5hours to see the boring full armor ending.

POKEMON (Red or Blue)

One Time only Pokemon:
Mewtwo, Moltres, Zapdos and Articuno can only be fought once in the game, so if you fail to beat and/or capture them, you won't get another chance. If you do fail, simply reload your saved game and try again.
Once you beat the game, return to Cerulean City and head for the bridge to the north that held 5 trainers and was on the path to Bill's house. Go left to the water, then SURF into the cave. Mewtwo is waiting inside.

Super Mario Brothers 2 Japanese Game:
Score 300,000 points or over in the normal game and Luigi head will appear on the game selection screen. Click on him to play SMB for Super Players. You'll also unlock the Secret game "You VS. Boo!" if you score over 100,000 pts.

Move Blocks Upward:
When any piece but a line or a square is falling, hold Left and press A rapidly to start the piece moving upwards. Or, if the piece is near the right wall, hold Right and press B rapidly. The piece should be against the Left or Right wall for this to work. This gets harder to do in the later levels.