The Lighthouse Wolf
Note: All information seen below is unverified, and thus needs confirmation.
The Lighthouse Wolf has the form of a standard wolf, but its pelt is slightly darker (by a few shades). Other than that, it shares the same appearance. TLW appears to be harder to kill (2-4 rifle rounds) and is not scared by flares or distress pistols. He appears to spawn on the second or third floor of the lighthouse, but TLW cannot get down the stairs. It does not re-spawn after death.
To kill The Lighthouse Wolf, the best strategy seems to be to throw a flare to whatever floor it is on (to provide visibility) and to stay below or above the stairs to allow continuous shots from a rifle. The only way to get rid of TLW is via a rifle.