[Mithlas]

Thanks for the pointers. I don't have GURPS Horror, but Bane sounds precisely like the vulnerability.

Advantages:
Unkillable 1 [50]
Regeneration: Very Fast (Bane, rare: silver) [90]
Regrowth (Bane, rare: silver) [36]
Injury Tolerance: Damage Reduction 2 or 3 [50 or 75]
Injury Tolerance: Unliving [20]
Claws: Sharp [5]
Discriminatory Smell [15]

Disadvantages (uncertain application):
Vulnerability (Characters 161) [10] describes "take extra damage from a particular attack form". While I think treating damage as multiplied with regards to shock is appropriate, I don't think it necessarily fits as far as doing more damage.
Susceptible (Characters 158) is an alternative, but the book description indicates it only applies to common things like poisons, metal.
Secret (Characters 152) [30] Psionics and a couple other books (as far as I remember) treat Secret as half the advantages lost and disadvantages gained, but the core book reads "Monster...hated and feared regardless of actual disposition...liable to be hunted on sight" which is appropriate for monsters that can destroy villages as his progenitor did.
Low Empathy (Characters 142) [20] He's not actually terrible at reading other people, but he's very bad at dealing with them in any constructive or supportive manner.
Distinctive Features (Characters 165) [2] The book specifies "of your race", but he appears to be human except for bone ridges along his cranium, claws, and orange reflective eyes.
Fanatacism (Characters 136) is a possibility given that he'd sacrifice himself or any of his comrades, but Code of Honor and Obsession already seems to cover his goal of hunting down monsters.

Disadvantages (clear):
Obsession (Kill all monsters, SC 6) [20]
Callous [5]
Frightens Animals [10]
Loner [5]
Nightmares [5]
Bloodlust (monsters must all die now, -10%) [9]

Attributes:
ST 14, DX 11, HT 12, IQ 9
Secondary Attributes:
HP 15, Per 13, Will 9, FP 12

Will comment on how he and Extra Effort interact later.