Beat the Egg Throw, Crane, and Quick Draw to get them on the start screen. Start up the game and go to your file and you will be able to play them as much as you want.
Final Level Secret
At the Last level (7-6) before going into the final door, press up and fly up to the moon and go under it. There will be a secret door there. Then just fall with the full life and one up. There will be the final secret room.
Five Extra Lives
In Rainbow Resort, jump or fly up to the ledge above the entrance. Stand directly over the door, then fly up. You will enter a hidden door. You skip the first three mini-bosses, and after beating the last one (Lion), you will enter a secret room with five 1-ups. Enter the door to your right to exit the level.
Grape Gardens Warp
Go to Grape Gardens: Door 6. Beat the Mike enemy. Do not swallow him. If you go to the next room, swallow the first light enemy you see. Turn around and walk back (not very far), and you will see a door. Go through the door and you will see a button. Press it to make a warp appear in Grape Gardens.
Nearly unlimited 'Mike' Ability
Obtain the "mike" ability and find any of the secret switches used to open up more areas. Use the ability two times first and then use the third time on the secret switch. You must jump from above and be very close to the switch as you use the mike. If the glitch worked correctly, when it shows what item you have, it should display "00" for item usage and you can use the ability an additional 266 times. If it failed, then you either did it too early or hit the switch before you used the ability.
In World seven, Stage two, there is a secret room. Fly up above the ledge and you will warp to the 4th Mini-Boss in the stage. Once you defeat the last Mini-Boss, Fire Lion, you will enter a room with five lives.
Thirty lives in the Goal Game
To get thirty lives in the Goal game, land on 7 then 6 then 5 then 4 then 3 then 2 and finally 1 in that order every time you clear a level to get thirty lives.