I've done level 6 and am a bit happy with it, it's twisted, you have to think fast thanks to downward vents and an inconveniently placed switch, and if you don't you lose access to the extra life! and/or you lose one!
It's also the first level I can commit without touching the core engine, which must mean something's good in it!
Commit: https://github.com/colinleroy/a2tools/commit/841822c22a0e3abc879c8d023894c32110f3cea9