WCW Nitro
All Secret Characters - Method 2
While at the screen where it says "Start" or "Options" press:
Right-C, Right-C, Right-C, Right-C, Left-C, Left-C, Left-C, Left-C, R, R, R, R, L, L, L, L, Z.
If the code was entered correctly you will hear Macho Man say, "Oh Yeah"
Credit Goes To: Tommy Murray via IGN 64

Dancing Wrestlers
Press B + C-Left at any time while on the Disco stage to make your wrestlers do the Y.M.C.A.!
Credit Goes To: Chris Zettler (Zettler@snsnet.net) via IGN 64

 All Secret Characters
 Dancing Wrestlers
 All Rings
 Big Hands
 Big Head Mode
 Big Body Parts
 Ring Select
 Swelling Heads
 Unlock All Characters
 Call For Backup
 Unlock Hidden

All Rings
At the title screen press c-left, L, c-right, R, Z. A sound will confirm a correct code entry. The new rings include Graveyard, Spaceship, Circus, Hive, Turbo, Wunderland, Boudoir, Hall of Mirrors, Rec Room (this is my favorite! you get to wrestle on a pool table!), Psychodelic, Disco, Jungle, 1984, Quark, and Texas.

Big Hands
At the mode selection screen, press L seven times then press C-Left 17 times. A tone will confirm the code.

Big Head Mode
At the title screen, press C-Right(7), R, Z. If you entered the code correctly, you will hear a sound. A tone will confirm the code.

Big Heads, Hands, and Feet
At the title screen, press R seven times, then press C-Right, Z. A tone will confirm the code.

Ring Select
At the options screen, press C-Right, R, C-Right, R, Z. From now on, every time Z is pressed, the current ring will advance to the next in the series.
To move in reverse, press C-Left, L, C-Left, L then press Z until you reach the desired level.

Swelling Heads
At the title screen, press C-Left seven times, then press L, Z. This will cause the wrestler's heads to sweel with each hit. A tone will confirm the code.

Unlock All Wrestlers
At the title screen, press C-Right 4 times, C-Left 4 times, the R button 4 times, the L button 4 times, and then Z. Then at the character select go to the top row of wrestlers and press UP. Repeat this process over and over until you get back to the screen with the original wrestlers.

Call for Backup
Press the Z button at any time during the match to cause a run-in to occur.

Unlock hidden Wrestlers
Beat the Tournament Mode with any wrestler on Normal or Hard and you will unlock a hidden wrestler. Each character will unlock a different wrestler, so try beating the game with everyone for the maximum lineup.
Credit Goes To: IGN 64