Tentacles only appear in Shiurath's level and seem to be a part of his body. They appear together with the eyes after walking halfway into the level. They hardly move and have high defense and health, making them annoying obstacles if you are relying on slow ranged attacks. On the other hand, if you have a high defense and damage they can be used to gain experience and level up.
Spyglass Buff Edit
"Tentacles are really clumsy! I think I can dodge them..."
+30% to dodge physical attacks vs. Shiurath.