Light World Edit
This level consists of a rapidly disappearing set of key blocks, A few sets of sawblades and not much else. For the first half you'll want to make short hops followed by a medium jump. The second half has ever higher jumps that need to be made. Basically weave your way through the saw blades and be quick.
Dark World (7-6X Bone Machine) Edit
This level has a similar concept to it's light world equivalent except the level is now vertical with the key blocks allowing for wall jumps. At least by cotton alley standards, this level is relatively easy if you've mastered wall jumping. Just snake through the sawblades and get to Meat Boy
Expert Remix (I-19) Edit
You are again going horizontally, your primary foe is the laser beams. Normally you're supposed to go right then left on the lower platform. There's a cheat however that if you drop through the first platform (while the laser's off) down to the lower platform you can easily beat it in 4 seconds