In "Mistaken" playing a Cyclops agent is a little bit like playing FIST on hard-core mode. PCs are a little darker and grittier and they have a lot more to balance than just saving the day without dying.
There are mechanical additions that you could compare with "sanity" from the Call of Chuthlu rpgs. Players can only commit so many war crimes before they either become NPCs or take their own life in despair.
This zine is full of prose that really gets you in the mind of an Cyclops agent which is fun to read. If you want to add some survival elements or alternate role play tools to FIST you should check this out.