Board Thread:Questions and Answers/@comment-212.78.8.30-20130624092807/@comment-24013632-20131031043420

I am having trouble obtaining the second key. on the 3 wave of that level the mechanical nightwalkers appear but for some reason one of them doesn't die I kill the rest and one has about 10 percent health left. I try using different guns but I still can't kill it. I need help. is there a secret to this?

Thank you in advance