Getting the Key
Near the start, a notification block informs you that the level changes based on the time remaining. In order to obtain the key (which will get you to Chocolate Secret), you need to complete the level in as little time as possible. (Timer must read at least 250 at the second pipe) First, jump on the chocolate platforms in front of Mario, and get over to the far right. There you will find a green pipe. Take the pipe, and if you get to an area with many red koopa paratroopa's, you are nearly done. If not, you will not get the key.
Once again, speed is a priority, so use the Koopas as your platform. If you have a cape feather and a Yoshi, this area should be a snap, since Mario can glide on top of each of his foes, which then extend his jump. If you lose Yoshi, however, don't be afraid; It's still possible to get the key.
Once you've completed this area, you should finally happen on a large number of Chucks that are throwing Baseballs toward Mario. If you do, then you will soon have the Key, which is located about 4 blocks away from the keyhole. Congratulations!
Complete move to the green tube at the end of the first screen (lower right) with less than 100 seconds of game play remaining to find the alternate exit.