Mock Darth Vader of The Empire Strikes Back

In the Empire Strikes Back, I dont understand the one scene when the mock Darth Vader appears. It can't be Yoda's cause he had no materials to build it, and it couldnt have belonged to the empires because then they would know where Yoda is and go and kill him. Also why did Yoda tell Luke he didn't need hissaber where clearly if he didn't bring it he would be toast. Can someone explain this?

edit - I suck at modding

 

This Thread Might Help.

 

Yep, see that thread.

 

You forget to hit the lock button again, Matt?

 

I thought this thread was gonna be about someone mocking DV!