Monster hunting without knowledge is nothing but a waste of time . . . and lives. [GURPS Monster Hunters 1: Champions, p. 16.]
Useful Hidden Lore Specialties
Angels
Cryptozoology (lake monsters, unicorns, etc.)
Demons
Free Spirits (fae, in-betweeners, etc.)
Restless Undead† (ghosts, zombies, etc.)
Lycanthropes
Mummies†
Mythos (elder gods, great old ones, etc.)
Sacred Places (ley lines, Atlantis, etc.)
Vampires†
† The Mummies, Restless Undead, and Vampires specialties of Hidden Lore default to each other at -3.
Useful Theology Specialties
Abrahamic (angles, demons)
Shamanic (free-willed spirits, ghosts)
Voodoo (free-willed spirits, zombies)
Other Useful Skills
Animal Handling* (cryptids, lycanthropes)
Archaeology (mummies)
Diagnosis (parasites)
Esoteric Medicine (cryptids, lycanthropes)
Expert Skill (Natural Philosophy) (cryptids, parasites)
Psychology (witches)
Thaumatology (witches)
* A particular specialty can be used against appropriate creatures; e.g., Animal Handling (Dogs) against a dire worf – though usually at a penalty.