
It's one of those bonus stages where you can keep jumping on the Klaptraps to knock bananas out of them. Well, I found that if you keep jumping on them without hitting the ground, you can keep getting extra lives if you bounce off of enough of them. Just jump on the any of the three Klaptraps, then jump on another one that's not flashing. Then jump on the third one. The first one you jumped on will no longer flash and you can jump on it again. Just repeat until you get a TON of lives. (This trick is similar to that extra life trick in SMB3 where you jump on Dry Bones repeatedly in World 2-Fortress, if anybody cares.)
Here's an old video of me doing the trick here (starts at around 0:34):
http://www.youtube.com/watch?v=qStQaE7SeEM#t=0m34s
I mess up near the end, though, because the Klaptraps go too fast... Actually, I don't think I've ever done it perfectly...