You can use part of your tail as a natural weapon attack.
Benefit(s): You can use a portion of your tail as a natural attack that deals 1d6 points of bludgeoning damage. This is considered a primary attack unless used as part of a full-attack action with attacks made with weapons (in which case, it is considered a secondary attack). Primary attacks are made with the creature’s full base attack bonus and add 1 1/2 times the creature’s Strength bonus on damage rolls. Secondary attacks are made using the creature’s base attacks bonus –5 and add only 1/2 the creature’s Strength bonus on damage rolls.
Sandy Petersen’s Cthulhu Mythos, © 2017, Petersen Games; Authors: Sandy Petersen, Arthur Petersen, Ian Starcher.