Four Tentacles are fought during the A Shadow over Ashdalequest while on a ship known as "the Empress". They attack players who are close to them with typeless damage, and once all four of them are defeated, Agoroth will emerge. Damage to them is capped at 40.
Two tentacles will be present during the fight with Agoroth, and while they can no longer be attacked, they can still damage players if they get close enough.
The tentacles usually retreat after 200 damage has been done to them. However, if a player is using fast weapons and uses a combat ability at the right time, it is possible to actually kill the tentacle for a small amount of XP.