Since there are so many pages on this fourm, I will save myself the trouble and ask very plainly, is there a guide for beating all of the story, conquest, and special ops maps with "double down" turned on?
I have already beaten the first 6 story levels and Loki with it on (without the Thor, too ;D), by the way.
Nope. There has been lots of discussion - a long time ago - but I doubt there was a single consolidated thread. You may have to use advances search and ferret out the threads.
Not a single consolidated thread as far as I know, either, but I do seem to recall that the user Mare posted a video of every single non-custom map on double down and by quickly checking my PMs for the one specifically regarding the Gump map, I see that this was done in the MalformationOfFear99 channel on youtube.
EDIT: Actually, these were posted in a single thread (http://knucklecracker.com/forums/index.php?topic=3965.0) even though the title does not clearly state that they were played on DD mode. It also looks like the video for Loki without Thor was removed for copyright issues.