I'm running a game this weekend for some friends, planning a one shot to take a break from our curse of strahd run. The vision is to use the basic Cairn rules, with some modifications to run a game with a similar feel to Sirenhead Resurrection, though using my own creature. I don't want it to feel like a sirenhead game, just using that game as inspiration. Does anyone have any suggestions of rules or mechanics to use, or how to keep the tension in a forest survival, sans magic game for some pretty traditional 5e only players?

Side Note: the creature I plan to use is a very large spider-esque creature, without a clear face. It absorbs the area around it, with trees growing out of its back, boulders protruding from its limbs, and even cars poking through its flesh. The head portion of the creature is made from rotting human skulls, with only a thin piece of flesh stretched across it, with an opening of jagged rock teeth, which it uses to consume living creatures. It's goal is only to grow in size, and eat as much as it can to do so.