At Character Select screen, press V 4 times, SPACE 4 times, Q 4 times, and T 4 times. Then press H to open up all the characters.
Big Head Mode:
At the Select Mode screen, enter V 7 times, Q, H.
Big Head, Hands, Feet:
At the Select Mode screen, enter Q 7 times, V, H.
At the Select Mode screen, enter SPACE 7 times, T, H
At the Options Menu, press V, Q, V, Q, H. Each time you press H, the ring will advance by one.
At the Main Menu, press SPACE, T, V, Q 4 times, then press H.
At the Main Menu, press SPACE, T, V, Q, SPACE, T, V, Q, and H. Now you have the secret rings.
Highlight a wrestler at the Character Select screen and press SPACE, V, T, Q, SPACE, V, T, Q, and H.
While playing in the Disco ring, throw your opponent out of the ring. Hit T and the wrestlers will do the YMCA. If you do it long enough, the wrestler will get counted out and you will win!
Thanks to Revolution readers Adam Koenigsberg, The_Hydester, Johnny M, Kane, Xpac21 44, Roaddogg, John, Matthew Swoboda, Josh Temple, Jesse Seymour, The_Hydester, Dirck James, Kevin Nash, and Tony Sink!