Altered Beast

Level select:
Hold A and press Start, select a level and hold X + Start at the title screen.

Options menu:
Hold A and press Start at the title screen.

Sound test:
Hold X + B + Up/Right and press Start at the title screen.

Beast select:
Hold X + A + B + Down/Left and press Start at the title screen.

Continue game:
When you've died, hold X and tap Start until restarting.

Two-player mode:
Press Start on controller two to begin game play.

Interactive credits:
The credits will appear after Athena is rescued. Punch or Kick the credits to force them to scroll downward.

Higher jumps:
While jumping hold Up and press kick.

Defeating the final Boss:
When you get to the Boss, duck and shoot your fireball. This is easy because he uses his arms more than his legs he will only kick with about one in every ten punches. Note: You will still get hit jump back and forth if needed


Virtua Cop 2

Big head mode:
Beat the game on easy. Then, press X, A, Y, B, B, B, Up, Up, Up, Up, Up on controller D.

Mirror mode:
Beat the game on the normal. Then, press L, Left, L, Right, L, Down, L, Up, R, Left, R, Right, R, Down, R, Up on controller D.

Random mode:
Beat the game on the hard. Then, press B, Left, X, Y, X, Y, B, A, B, A, Right, Left, Right, Left on controller D.

Play as Janet:
Start a new game and select a stage. Then at the file screen, hold Start until the mission begins to play as Janet


Golden Axe

9 continues:
At arcade mode, hold Down/Left + X + B, release and press Start.

Level select:
At arcade mode, hold Down/Left + A and press Start at the character selection screen.

Two-player mode:
Press Start on controller two to begin game play


Sonic The Hedgehog

Level select:
Press Up, Down, Left, Right at the title screen, then hold X + Start.

Bonus points:
Complete Green Hill Zone 1-1 or 1-2 in 29 seconds or less to receive 50,000 bonus points.

All Chaos Emeralds:
(submitted by: BigTommyGUN)
Enable the "Level select" code, then choose the "Bonus level" option on the level selection screen. Obtain the Chaos Emerald, reset the game, and repeat the process until all of them are in your possession. Allow the game to continue after obtaining the last Chaos Emerald to start in the Green Hill Zone.

Debug mode:
At the title screen, press Up, A, Down, A, Left, A, Right, A, Start, then hold X. Continue to hold X until the game begins. Screen coordinates will appear instead of a score and the number of objects displayed will appear instead of the time remaining. Use one of the following controller actions to enable the debug code:::

Change objects:
Press A during the game to change Sonic into a game object. Press X to change into a new object. Press B to place an object on the screen. Press A again to revert back to Sonic.

Invincibility:
Sonic is, by default, invincible in debug mode.

Slow-motion:
Pause the game and hold A.

Restart:
Pause the game and press X.

Frame advance:
Pause the game and press B

Infinite lives:
Collect the extra life at the very bottom of Green Hill Zone - Act 3. Accumulate 100 rings to obtain another extra life. Collect a third extra life located at the top of the loop-the-loop. Intentionally lose a life and repeat the process.


Streets Of Rage 2

Cheat mode:
Highlight Options, hold X + A on controller two, then hold B on controller one


Revenge Of Shinobi

Infinite shurikens:
Select the Shurikens on the options screen, set it to 00 and wait for ten seconds.

End bonus:
Complete any level with a number of shurikens equal to 11 times the number of remaining lives to add 30,000 bonus points to your score


Vectorman

Debug mode:
At the options screen, press X, A, A, X, Down, X, A, A, X to display a debug menu, including level select.

Full health:
Pause the game and press X, A, Right, X, B, X, Down, X, A, Right, X.

Slow-motion:
Pause the game and press Down, Right, X, B, Up, Left, X.

View map coordinates:
Pause the game and press A, X, Left, Left, or A, X, Left, Down.

Free movement:
Pause the game and press B, X, Left, Left, X, B, X, A.

Collision detection dots visible:
Pause the game and press X, A, X, B, X, A


Phantasy Star 2

Slow-motion mode:
Pause the game while in the countryside by holding Start + A. Keep A pressed to move in slow-motion.

No opponents in dungeons:
Continuously press B to display the control menu and press A to close it while holding the D-pad in any direction


Columns

Second magic jewel:
Create one row of normal jewels stacked almost to the top of the playfield. Allow a vertical space for only two of the three jewels in the next block to fit. Watch the preview window for the next magic jewel block. When it appears, quickly move it to the top of the prepared stack. The magic jewel will eliminate the "touching" color jewels, and all of the remaining jewels will drop down, as will the single magic jewel that was off the playfield. This single magic jewel will drop down and eliminate another group of colored jewels.

10,000 bonus points:
Create one vertical column that is empty all the way to the bottom of the playfield. Watch the preview window for the next magic jewel block. Position it in a way so it falls down this column to the bottom.

Create magic jewel:
Begin a game in easy arcade mode. Fill the two columns on the far left or far right as high as possible with jewels to create a magic jewel


Sega Swirl

Higher score:
Execute a big move, then pause the game during the animation and choose to restart. The move you just did will register on your new game