the short and approximate answer is that cephalotoxin is a neurotoxin for crustaceans but doesn't have much impact on vertebrates, although injecting any random protein into yourself risks allergic reactions or infections from the wound.
A toxin purified from the PSG of Octopus dofleini (Songdahl and Shapiro, 1974) gave a single constituent toxic to crustaceans. Its molecular weight indicated by SDS-polyacrylamide gel electrophoresis, was 23,000 ^ 1000 Da.
In general, coleoids that aren't blue-rings or Eledone cirrhosa have a variant of cephalotoxin, which is neurotoxic to arthropods and probably other invertebrates (it causes tonic paralysis like many insecticides do) but not toxic to vertebrates.
Has mototi been confirmed toxic? That's the one that the local natives say is poisonous, right? I can't find any refs in google scholar that describe its toxin, but rumors of toxicity seem like a good reason to avoid bites, of course.