Not to be confused with Tentacle (NPC).
[FAQ] • [doc]

A tentacle is part of a five part swamp creature encountered during the Temple Trekking minigame on the hard path. They can always hit players on the boat even though they are not directly next to them. They can do quite a lot of damage so Protect from Melee or Deflect Melee may be helpful. If all four tentacles are not killed before the Head, the head will regenerate.