|Most of these extra/secret levels, I got 100pts easily just by exploring more thoroughly and not playing badly.|
Secret 3 had some really tricky parts. There's this digging tunnel where you have just enough time to dig through the dirt with the mole transformation, and then you have to use a nearby helicopter transformation bubble to go through the rest of that tunnel to get to a flower... and then another flower that had me stumped for a while, until I found the only way to get to it is to go underneath the ground with another helicopter. The transformation bubbles here are 1-time-use only, so you pretty much have to restart the level again after figuring out what to do.
Extra 3 is a very short, but very difficult level, and the red coin I was missing last time was a fly guy that flies away before you see him if you take too long moving forward. this level really makes me want to take it slow in order to kill all the monkeys because of how easily you can get hit by their projectiles and fall off.
Secret 5... This is the weird one that seems to require using a bunch of the items that you get from winning bonus games. I figured out you can get up to a higher part of the first section by freezing the spikey enemies and then bouncing off them... but that section with the pipes and ice cubes, I still can't figure out where to go there... I think I might actually need a guide for this one.