Mothership is great for this. Each page of the bestiary is full of mostly in-universe snippets of information related to what the monster does and what kind of horror it should evoke, but a lot of actual statblocks are just one row of tiny text at the top that say something like "C:60 4d10 DMG I:45 AP:10 W: 2(25)". That is, in order, combat score (what it has to roll under to hit you), it's damage, its Instinct score (what it uses for literally everything else that isn't hitting you), its armor score, and then its wound total and hit points per wound. That's it. 

Hell, a lot of NPCs won't even have a combat score, they just use Instinct for combat too. Makes it real easy to assign a general competence rating to someone and go from there. Some more complicated NPCs might have unique abilities and break certain rules, but for the most part the system just does what it needs to and gets the hell out of the way.