You found the HammerTestLevel. Fantastic job! ;-)
It used to be in bronze, so imagine the horror of that! Try the jetpack+sword technique against them. Once you get their timing down, that map is actually pretty easy although I will agree it comes as a bit of a shock if you are not expecting it. It's all part of the randomness of endless mode. The more you play it the more familiar you get with what to expect and how to plan for it accordingly. Hopefully with some of that comes more fun than frustration. If the HammerTestLevel gets too much negative feedback we will probably consider moving or removing it from Endless.
-Cheers