In the middle of the game, press pause and type "BANG". 

play as gold dural:
In the character selection menu, press DOWN, UP, RIGHT, then DEL+LEFT. 
You should here a confirming sound 

play as silver dural:
In the character select menu, press DOWN, UP, RIGHT, then DEL+LEFT 

add dural to the records screen:
At the start screen, press UP 17 times, then press ENTER. Go to the 
options screen, and you should hear "RING OUT!". 

slow motion replaying:
At the end of the round, hold DEL+END+PGDN before the character does their 
victory stand 

choose victory phrase:
Hold either DEL, END or PGDN, and you can choose 

stage select and ring size:
At the start screen, press UP 12 times, and press ENTER. Go to the options 
menu, and you should here "K.O.!". Move the cursor to the exit, and press 
down once more to make the cursor disappear. Press DEL and a second options 
menu will appear.