As far as The Deadly Garden goes, I didn't think you had to kill the Lurkers and Slows at the same time, but how else do you logically satisfy both conditions at once? What I mean is, if you're supposed to kill the Lurker before any other type of Gray AND kill the Slow before any type of Gray, don't they sort of cancel each other out since both Lurkers and Slows are each types of Gray? Or does it mean before any regular, non-special Gray?
At any rate, I killed the Slow grays first, then I killed the Lurker, then everything else, and none of the objectives triggered.
Sorry if I was unclear. It was kind of late when I wrote that.