I'm trying to get Girl Boy, and I only die in 3 levels

Does anybody have a good tip how to pass the Tunnel Blower, Hopscotch and 4 Letter Word in less than 3, maybe 4 kills...

I don't know if this will be any help, but for Hopscotch I prefer to do it the "less bouncy" way. I try to get Bandage Girl stabilized and just keep practicing the "to the left, then under" move for the top saws. After you do one, you can stabilize Bandage Girl by moving a bit to the right (where there's less repulsion) until she stops going up, then back to center. Even then, it's still a hard level, but I guess it all just comes down to practice. Also, you can do a running start under the first saw if you time it right.
Just got Maggot Boy and to be honest it wasn't as bad as I was thought it would be once I had a plan and practiced the levels that gave me trouble.
Route: 9-10, 15-20, 1-8, 11-14.
Grinding Mill - I used Captain Viridian and found a neat little bug with the zombie AI. So of course you reverse at the start and wait for the key to drop, then move across the key shaft to the right zombie spawn. Then, if you jump to the right, the zombies will never jump into you (they'll jump, but it'll be once you're falling down). Lead them into the saw, reverse and get the key, reverse again so you're on the ceiling of the platform Bandage Girl is on, then you can do a jump to the opposite wall and 2 walljumps to victory.
Rotgut can of course be broken with Naija. For The Witness, I used Viridian again. From the first alcove you can jump through the saws easily, then the rest is just reversing between saws.
These next 3 levels use The Kid's "run off the platform and double jump" trick. On Rise, once you get up to that ledge below the first repeller, jump, then do a delayed double jump. This will let you get to the left wall easily. On 10 Horns, you can do the same trick on the last part, and on King Carrion you can reach the right wall from the start.
I think that's it. Now onto the more ridiculous achievements.