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

Stage select and ring size:
At the start screen, press UP(12x's), 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.

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

Choose the victory phrase:
In the character selection menu, press DOWN, UP, RIGHT, then DEL+ LEFT. You should here a confirming sound.