I think it'd be useful to collect anecdotal evidence from people who have run this game about what event / invader / spawning combinations people used to take down their players on particular missions. I ran mission 1 over the past weekend and was completely decimated as the invader. Turns out its generally agreed (even by the designer) that mission 1 with the suggested cards is pretty favorable for the marines. I know having the imps spawn in close quarters with the chainsaw was a terrible time for myself. The designer suggested as a soft nerf to remove a handful of the early health packs from the mission set up to balance it better. I'm sure running a different set of demons would also help (and not provide Imp fodder for the chainsaw)
Anyway -- any advice from successful invaders on what you ran or what strategies you employed on any particular mission to slaughter your players?