As I try my hand at something that is largely a pure dungeoncrawl with NGR (the Northcote/Hogswamp sci-fi game) I've been working with an alternate solution to wandering monsters.
Currently I've been using the Stealth System (mess up on stealthy actions or make noise, build suspicion, get caught) to work as a "build up to wandering encounter" check. This has been working pretty well so far, players are free to crank radios, use dynamite, rev chainsaws and fire guns all they want, and slowly it builds into someone or something coming to investigate.
This also works well as a balance for rogues in a game where everyone can disarm and detect traps. It has the advantage of letting PC's freak themselves out about the amount of noise they are making in a concrete way, adding to a rising sense of tension. What is about to crawl out of a pipe or through the air vents towards them? Convicts? Trained Killers? A stray cat? Nothing? They know something is about to risk appearing if they take 1 more suspicion..
What do you do? Take the risky action? Burn through your luck to avoid being caught (but be weaker when something does appear when you push into another room in ten minutes?) , or do you fall back to a safe haven and recoup?
Merry Christmas M.R. James
11 hours ago