The Fog-spawn (or Thing in the Fog) is an other-dimensional creature from the Masks of Nyarlathotep campaign for Call of Cthulhu. If you’re a player in that campaign, turn back now: there will be spoilers!
Here’s how to learn a new RPG system. Or at least, how I learn a new RPG system. In brief: skim through the book, practice making some characters, read the book more carefully, run a one-shot, make cheatsheets, and then run that campaign.
Campaigns can be huge games which last years. Players might come and go. People’s tastes might change. What you decided the campaign would be about one, two, or more years ago might not be what the players want any more. So, hold a mid-campaign check-in to ask about how everyone is finding the game and whether anything needs to change.
1d12 + 1d8 table is commonly used for
random encounters, because it gives a nonuniform distribution where
some outcomes are more likely than others. But why stick to that?
By rolling one of the dice with advantage or disadvantage, you get
a very different distribution, and can make one table work in many
A lot of GMs advise rolling behind a screen, so you can fudge rolls when you get a result which would be bad for the story. I think that at best fudging is unnecessary, and can be remedied by being more thoughtful about what rolls you ask for (and I go in to how I think about rolls), and at worst cheating, where you’re explicitly ignoring the rules of the game.