Farming SE20 from Cold Sharks is not feasible currently. I have killed thousands of Cold Sharks and received more than seven copies of every other mastery book. I could easily be convinced that they do not actually drop SE20 and the monster book is displaying incorrect information, but a guildmate told me that he got one after 10,000 or so kills, which I choose to believe. But this is dumb. Either increase the drop rate to a more reasonable number, or remove it to prevent people from getting false hope.
I got 2 under an hour when I last tried farming it. Also @Tect got like 3 or 4 in an hour. It's just RNG I guess. Might be better off buying it from FM if it isn't dropping for you, and use the time to farm at ulu1 instead.
I hunted the last 10 days at cold shark and it dropped nothing. But i hunted yesterday at cold sharks and it dropped 3 books in an hour.
The RNG is real, I once spent more than a day to get one SB, and after that, i got the second and third SB in less than an hour. Also god damn you darren @Tech
They most certainly do drop, you just think they don't because there aren't many cold sharks in the map as regular sharks. I've gotten lots from cold sharks and pianus left