There seem to be a lot of solutions still to be found for levels that are already "done"; for example, I can add the following:
Crazy 13: climber+miner+digger (pretty much the standard solution, unfortunately not 100% since the climber mines through the floor). Also, improved the currently listed combination (builder+miner+digger) to 100%, replay attached.
Crazy 15: climbers+builders (direct drop glitch), builders+diggers improved to 100% with glitch (replay attached - glitchless falls short of 100%, so "glitch for 100%").
edit: Crazy 18 with 3 types:
- builder+basher+miner improved to 100% (also good for min skills/max % - it's 6 skills, same as for the regular least-skills challenge)
- bomber+builder+basher
- bomber+builder+miner
- blocker+builder+basher
- blocker+builder+miner
Replays are attached. Most rely on one crucial observation that (as far as I can tell) hasn't been picked up on before:
The vacuum trap can be disabled with a single brick.
edit2: Crazy 19 with 3 types:
- builder+basher+digger improved to 100%
- bomber+builder+basher
- bomber+builder+digger
- blocker+builder+basher
Again, replays attached.
edit3: Crazy 20 can be done with bombers+builders. Nothing replay-worthy here, just a whole lot of bomber timing.