Ninja magic or wisely placed claymore mine? My guess is that the Ninja family knew to carry some sort of practical bag of magic tricks to escape situations…
Wondering who Miyamoto Mushashi is? Well, wikipedia sez: http://en.wikipedia.org/wiki/Miyamoto_Musashi
So dark bad ninja is calling upon the powers of one of the greatest warriors of all-time in the key of He-Man to weasel his way out of Ninja Dan? Not very book of the five rings… is it?