Six credits:
Hold Select and press I, II, II, I three times, II four times. The word "CREDIT6" will blink above the title to confirm correct code entry.

Expert mode:
Hold Select and press I, I, II, II.

Yellow mode:
Hold Select and press I three times, II three times, I three times, II four times.

Blue mode:
Hold Select and press I four times, II four times, I four times, II four times.

Green mode:
Hold Select and press I three times, II three times, I four times, II four times.

Usagi 5 mode:
Hold Select and press I five times, II, I five times, II, I five times, II.

Shield 5 mode:
Hold Select and press I nine times, II eight times, I seven times, II six times, I five times, II four times, I three times, II, II, I.

Shield 4 mode:
Hold Select and press I four times, II three times, I, I, II.