Answer:
Well the Engineer is taken with the Friendly Phantom (dutch mickeys etc.) and after the credits Johnson talks to Dare while walking down the corridor and then sees the Engineer and gives him a lighter and Johnson gets a cigar out and talks to the alien and says " what are the covanant planning... tell us" and the Engineer lights his sigar and that's it :P
if you do it on Legendary it will have a Different ending see it for yourself..