Tentacles are tough! I've had one death to them during my first longish game when I went wandering around and thought I could take one on. In my current game, I just got a bunch of Mermen to attack the tentacles, and then when I wandered back into that area, there were a bunch of frog legs and tentacle drops littering the area. Usually I just run from the tentacles and avoid them...no need for me to kill them at this time.