Level 1: Kill All The Mice
Jump on the moving mouse, then on the cursor.
Level 2: Look Very Close
The third block up in the stack of seven can be passed. Go through it.
Level 3: And The Answer Is…
Walk into the question block and type "…".
Level 4: "You" Needs To Be Big
Hold shift and type "YOU".
Level 5: Click 500 Times To Escape The Trap
Level 6: You Need To Be Small To Exit
Level 7: Don't Give Up Yet
Walk to the lock and type "i give up".
Level 8: Retne
Level 9: It's In The Eye Of The Beholder
Click the man's eye.
Hit the number "4".
There are invisible walls around. Jump onto the block on the floor, then two stairs up on the right stairs, then left across. The best way is to trial and error.
Hit A, then type "Nazo Kyougi".