Deer in Scotland have begun biting off the heads of baby birds, sucking out their bones, and leaving behind deformed carcasses of deflated meat. Apparently they’re seeking to supplement the limited calcium in their diet (which they need in order to support the growth of their mating antlers)
But slap on a ritualistic patterning to the bird murders, and you’ve got the basic building blocks of a pretty decent horror scenario. (Or are the birds the real problem with the deer being enchanted by a local druid circle to stop whatever cuckoo terror is nesting on the island?)
Alternatively, crank up the stakes in a fantasy horror game: Replace “baby birds” with “actual babies”. Replace “deer” with “dire deer”. (Possibly deer who have become dire due to their blood-drinking rites. And what happens when the bloodcraze begins to spread?)