Have key to every level:
Quickly press A, B, A, B(2), A, Up before the "Start" and "Password" options are displayed at the title screen.

Level	Password
1-1	O88888
1-2	CVJB 8888
1-3	GVJD 8888
1-4	RVJH 8888
1-5	XVJS 8888
1-6	XVJY 8888
1-7	8VBY 8888
1-8	CYDY 8888
1-9	MYHY 8888
1-10	TYSY 8888
2-1	TZ8888
2-2	QZVJ B888
2-3	OZVJ D888
2-4	8ZVJ H888
2-5	?ZVJ S888
2-6	?ZVJ Y888
2-7	CZVB Y888
2-8	QZYD Y888
2-9	4ZYH Y888
2-10	KZYS Y888
3-1	KZZ888
3-2	6ZZV JB88
3-3	TZZV JD88
3-4	CZZV JH88
3-5	2ZZV JS88
3-6	2ZZV JY88
3-7	QZZV BY88
3-8	6ZZY DY88
3-9	XZZY HY88
3-10	RZZY SY88
4-1	RZZZ88
4-2	JZZZ VJB8
4-3	KZZZ VJD8
4-4	QZZZ VJH8
4-5	VZZZ VJS8
4-6	VZZZ VJY8
4-7	6ZZZ VBY8
4-8	JZZZ YDY8
4-9	?ZZZ YHY8
4-10	8ZZZ YSY8
5-1	8ZZZZ8
5-2	MZZZ ZVJB
5-3	RZZZ ZVJD
5-4	6ZZZ ZVJH
5-5	6ZZZ ZVJS
5-6	GZZZ ZVJY
5-7	JZZZ ZVBY
5-8	MZZZ ZYDY
5-9	2ZZZ ZYHY
5-10	CZZZ ZYSY
End	CZZZZZ

Hint: Secret rooms:
Get the wings to enter the secret rooms.