Pretty soon I'm planning on running a homebrew game based on Pathfinder rules for a "monster hunter" type game set in my home city of Baltimore where an Astral Rift starts letting weird things in from other world, and I'm trying to brainstorm ideas for interesting mysteries/encounters using monsters from the PF Bestiaries. I have one 90% fleshed out one so far (Note: characters are starting at 1st level for this, and it's very sandbox):
1. A woman is killed, her blood drained through three holes in her neck, and the red coat she was seen wearing earlier that night was stolen. An Ulgothol (Faceless Stalker, CR 4) crossed into this world through an Astral Rift, killed the woman and is now assuming her form to hunt new prey.
While this is going on, players may notice reports of large grey hounds, apparently stray, being seen in the area at night, as well as a rise in the number of missing dogs. A small pack of Blink Dogs (CR 2 allies) that was tracking the Ulgothol followed it threw the rift, and have been recruiting local canines to aid in its capture. These recruited dogs, some strays themselves, are "awakened" and eventually become blink dogs themselves.