Level Select and Secret Level 12
On the 2nd level, when you go to the third fireplace, skip all of the balloons and go to the front of the fireplace. Enter this code: Up, Up, Down, Down, B, Right, Left and then the screen will say "level skip?" select yes.
Time Machine
On level 5, go under the first table you see. Then jump under there. Then you're a level with Dodo birds.
Level Passwords:
2 - TQMMY QK
3 - RQVDHJVV
4 - BVBYFJND
5 - RJDBCVRT
6 - VNGBLJCV
7 - BJGSMVSH
8 - LJTBWQQD