Here's another fewer-builder challenge that is glitch-free:
Mayhem 17: A0;Save 100% using only 6 bridges. A0;Although, now that I think about it, it may be possible with 5 (I'll have to check). A0;It may be possible to lower the number even further with ccexplore's Tame 20 glitch, though.
I've confirmed the lowest number of builders you can get away with (at least on the PC) and still pass the level:
Mayhem 17: Save 96% (77/80) using only the following:
2 climbers, 2 blockers, 1 builder, 3 bashers, 2 miners, and 2 diggers
In other words, I have lowered the number of builders down to 1, at the expense of not saving 100%.
This is not the Tame 20 glitch; in fact, I'm fairly sure you will not be able to attain a Tame-20-glitch type of solution, using only one builder, that passes the level even if you're allowed to use all the other skills given. (But feel free to prove me wrong.) You certainly won't be able to do it with the fewer number of diggers and miners allowed here.
Instead another glitch is involved. Actually a fairly spectacular one, which unfortunately I definitely don't want to reveal at the moment. Somewhat reminiscent of the Tame 20 glitch, but a bit crazier and more powerful. Don't worry, I will reveal it eventually. I'll say though that it is generally very hard to apply (
much harder to apply than the Tame 20 glitch, for starters).
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About the skillset given above: I'm pretty sure you can trade in a miner in place of one of the diggers (so 3 miners + 1 digger instead of the 2+2 above). Using a 2nd digger might be slightly easier for timing-precision purposes, but then again it might just be a matter of practice in either case.
About 96%: conceivably there is a small possibility that you can achieve 97% with this basic solution, but it'd be extremely difficult to plan out a viable setup. You definitely cannot save more than 97% with this solution idea without using additional builders, barring as yet unknown glitches.
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As for a 100% solution using the least number of builders (all glitches allowed), it looks like you need 3 builders, and I do have such a solution in mind involving just the Tame 20 glitch, but I haven't tested it out yet. If that 3-builder solution works, it is straightforward to convert it into a 2-builder solution that saves 98%.
Given the new glitch I introduced here, I can't definitively rule out a 100% solution using only 2 builders, but it seems quite unlikely to me at the moment.
And finally, it looks like LemSteven's 5-builder solution is indeed the lowest number you can achieve for a glitch-free solution.