I'm basically unqualified to comment on monster balance due to lack of experience, but some thoughts:
-Lack of flight?
-The Vital Strike chain feels like it should get it's own line in the attacks list for comparison, or possibly be changed out for something else. Greater Grapple missing?
-Blood Curse feels like it has a strangely low duration for something described as a "curse", and feels like a place to inject some extra flavor. Perhaps drinking the blood of the Moon Presence cures the curse, which otherwise lasts indefinitely? I'm not super clear on Bloodborne flavor.
Numerically, comparing to the Pathfinder Bestiary, this has:
-Below-average AC by four points
-Will saving throw is way way higher than normal, by 10 points (probably OK given flavor though), but otherwise is around good.
-Saving throw DCs I'm uncertain about, except to note that the DCs on the spell-like abilities are way way lower than on the supernatural abilities.
-Attack bonus far above the median, by 13 points(!). Power Attack fodder indeed, especially since this doesn't really suffer from iterative attack penalties. Combined with the number of attacks, this deals out a heck of a ton of damage, almost guaranteed- assuming a +10 bonus from Power Attack, we have
-2 claws deal an average of 35 damage each
-6 tentacles deal an average of 32 damage each
-4 tails deal an average of 28 damage each
That's around 270 damage per round, which is far more than pretty much anything I can think of. Is this intentional?