The Best of the best of the BEST Skullmonkeys were chosen by Klogg to guard the Evil Engine itself (which is the only place where you'll find them).

With their jetpacks they fly around on their guarding pathes, which can be rather dangerous for someone who doesn't have a jetpack and has to use the tiny platforms to get along...

But actually, the REAL danger in Evil Engine #9 is the absence of ground, isn't it?